Inspection system by charged particle beam and method of manufacturing devices using the system

ABSTRACT

An inspection apparatus by an electron beam comprises: an electron-optical device  70  having an electron-optical system for irradiating the object with a primary electron beam from an electron beam source, and a detector for detecting the secondary electron image projected by the electron-optical system; a stage system  50  for holding and moving the object relative to the electron-optical system; a mini-environment chamber  20  for supplying a clean gas to the object to prevent dust from contacting to the object; a working chamber  31  for accommodating the stage device, the working chamber being controllable so as to have a vacuum atmosphere; at least two loading chambers  41, 42  disposed between the mini-environment chamber and the working chamber, adapted to be independently controllable so as to have a vacuum atmosphere; and a loader  60  for transferring the object to the stage system through the loading chambers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electron beam based inspectionapparatus for inspecting defects in patterns formed on the surface of anobject to be inspected, and more particularly, to an inspectionapparatus useful, for example, in inspecting defects on a wafer in asemiconductor manufacturing process, which includes irradiating anobject to be inspected with an electron beam, detecting secondaryelectrons which vary in accordance with the properties of the surfacethereof to form image data, and inspecting patterns formed on thesurface of the object to be inspected based on the image data at a highthroughput, and a method of manufacturing devices at a high yield rateusing the inspection apparatus. More specifically, the invention relatesto a projection type electron beam inspection apparatus which adopts aarea beam and a method of manufacturing devices using the inspectionapparatus.

2. Field of the Invention

In semiconductor processes, design rules are reaching 100 nm and themethod of production form is evolving from mass production, with a fewmodels, such as a DRAM, into small-lot production with a variety ofmodels such as a SOC (Silicon on chip). This has resulted in an increasein the number of processes, and an improvement in yield for each processis essential; which makes it more important to inspect for defectsoccurring in each process. The present invention relates to an apparatusto be used in the inspection of a wafer after particular steps in thesemiconductor fabrication process, and in particular to an inspectionmethod and apparatus using an electron beam and also to a devicemanufacturing method using the same.

3. Description of the Related Art and Problems to be Solved by theInvention

4. Description of the Prior Art

In conjunction with a high level of integration of semiconductor devicesand a micro-fabrication of patterns thereof, an inspection apparatuswith higher resolution and throughput is desired. In order to inspect awafer substrate with 100 nm design rules for any defects, a resolutionequal to or finer than 100 nm is required, and the increased number ofprocesses resulting from large-scale integration of devices calls for anincrease in the number of inspections, which consequently requireshigher throughput. In addition, as multilayer fabrication of devices hasadvanced, the apparatus is further required to have a function fordetecting contact failures in vias for interconnecting wiring betweenlayers (i.e., electrical defects). In the current trend, an inspectionapparatus using optical methods has been typically used, but it isexpected that an inspection apparatus using an electron beam may soonenter the mainstream, substituting for inspection apparatus usingoptical methods, given the requirements of higher resolution anddetection of contact failures. The electron beam method, however, has aweak point in that it is inferior to the optical method in throughput.

Accordingly, it is desirable to have an apparatus having higherresolution and throughput and being capable of detecting the electricaldefects. It has been known that the resolution of the optical method islimited to ½ of the wavelength of the light to be used, and it is about0.2 μm in a typical case of visible light being put to practical use.

On the other hand, in the method using an electron beam, typically ascanning electron microscopy method (SEM method) has been put to use,wherein the resolution thereof is 0.1 μm and the inspection time is 8hours per wafer (20 cm wafer). The electron beam method has thedistinctive feature that it is able to inspect for any electricaldefects (breaking of wires in the wirings, bad continuity, badcontinuity of via). However, the inspection speed (sometimes alsoreferred to as inspection rate) thereof is very low, and so thedevelopment of an inspection apparatus with higher inspection speed hasbeen eagerly anticipated.

Generally, since an inspection apparatus is expensive and the throughputthereof is rather lower as compared to other processing apparatuses, theinspection apparatus has been used after an important process, forexample, after the process of etching, film deposition, CMP(Chemical-mechanical polishing) flattening or the like.

The scanning method (SEM) using an electron beam will now be described.In the inspection apparatus of SEM method, the electron beam iscontracted to be finer (the diameter of this beam corresponds to theresolution thereof) and this fined beam is used to scan a sample so asto irradiate it linearly. On the other hand, moving a stage in thedirection normal to the scanning direction allows an observation regionto be irradiated by the electron beam as a plane area. The scanningwidth of the electron beam is typically some 100 μm. Secondary electronsemanating from the sample by the irradiation of said contracted andfined electron beam (referred to as a primary electron beam) aredetected by a detector, either a scintillator plus photo-multiplier(i.e., photoelectron multiplier tube) or a detector of semiconductortype (i.e., a PIN diode) or the like. The coordinates for the irradiatedlocations and an amount of the secondary electrons (signal intensity)are combined and formed into an image, which is stored in some recordingmedium or displayed on a CRT (a cathode ray tube). The above descriptionillustrates the principles of the SEM (scanning electron microscopy),and defects in a semiconductor wafer (typically made of Si) in thecourse of processes may be detected from the image obtained in thismethod. The inspection rate (corresponding to the throughput) is varieddepending on the amount (the current value), beam diameter, and speed ofresponse of the primary electron beam. A beam diameter of 0.1 μm (whichmay be considered to be equivalent to the resolution), a current of 100nA, and a detector speed of 100 MHz are currently the highest values,and in using those values the inspection rate has been about 8 hours forone wafer having a diameter of 20 cm. This inspection rate, which isextremely low compared to the optical method (not greater than 1/20),has been a serious production problem (drawback).

Also, in regard to the prior art of inspection apparatus related to thepresent invention, an apparatus using a scanning electron microscope(SEM) has been commercially available. This apparatus involves scanningan object to be inspected with a fine electron beam at very narrowintervals of scanning width, detecting secondary electrons emitted fromthe object to form a SEM image, and comparing such SEM images ofdifferent dies at the same locations to extract defects of the objectbeing inspected.

Conventionally, however, there has been no electron beam based defectinspection apparatus which is completed as a general system.

A defect inspection apparatus which applies SEM requires a long time fordefect inspection. In addition, increasing the beam current to improvethroughput would cause a degradation of the beam due to the space-chargeeffect and charging on the wafer with insulating material formed on thesurface thereof, thereby failing to produce satisfactory SEM images.

Hitherto, no proposal has been made for the overall structure of aninspection apparatus which takes into account the combination of anelectron-optical device for irradiating an object to be inspected withan electron beam, with other subsystems associated therewith forpostioning the object to be inspected to for irradiating by theelectron-optical device in a clean state, and for aligning the object tobe inspected. Further, with the trend of increasing diameters of wafersto be subjected to inspection, the subsystems are also required to copewith wafers of such large diameters.

In view of the problems mentioned above, it is an object of the presentinvention to provide an inspection apparatus which employs an electronbeam based electron-optical system, and achieves harmonization of theelectron-optical system with other components, which constitute theinspection apparatus, to improve the throughput.

It is another object of the present invention to provide an inspectionapparatus which is capable of efficiently and accurately inspecting anobject by improving a loader for carrying the object to be inspectedbetween a cassette for storing objects under inspecting and a stagedevice for aligning the object to be inspected with respect to theelectron-optical system, and devices associated with the loader.

It is a further object of the present invention to provide an inspectionapparatus which is capable of solving the problem of charging,experienced in the SEM, to accurately inspect an object.

It is a further object of the present invention to provide a method ofmanufacturing devices at a high yield rate by inspecting an object suchas a wafer, using the inspection apparatus as mentioned above.

Also, with increasing integration of semiconductors, there has been aneed for a sensitive inspection apparatus to be used in thesemiconductor device manufacturing process for defect inspection in thepattern or the likes in semiconductor wafers. In this regard, there havebeen electron microscopes used as the inspection apparatus for suchdefect inspections, as disclosed in Japanese Patent Laid-openPublications Nos. Hei 2-142045 and Hei 5-258703.

For example, in the electron microscope as disclosed in Japanese PatentLaid-open Publication No. Hei 2-142045, an electron beam emitted from anelectron gun is converged by an objective lens to irradiatea sample tobe inspected, and secondary electrons emitted from the sample aredetected by a secondary electron detector. In addition, in this electronmicroscope, a negative voltage is applied to the sample, and further anE×B type filter is arranged between the sample and the secondaryelectron detector, said filter having an electric field and a magneticfield crossed at right angles.

With such a configuration, this electron microscope allows a highresolution to be obtained by decelerating the electrons irradiated ontothe sample by way of the negative voltage applied to the sample.

Further, the application of the negative voltage to the sample helpsaccelerate the secondary electrons emitted from the sample, and theaccelerated secondary electrons are further deflected by the E×B typefilter toward the secondary electron detector, thus to be efficientlydetected by the secondary electron detector.

In those conventional apparatuses using the electron microscope asdescribed above, the electron beam from the electron gun is keptaccelerated to be highly energized until just before it impinges ontothe sample, by a lens system such as an objective lens with a highvoltage applied. Then, the negative voltage applied to the sampledecelerates electrons impinging upon the sample, thus allowing a highresolution to be achieved.

However, since the high voltage is applied to the objective lens, whilethe negative voltage is applied to the sample, there has been a riskthat an electric discharge may occur between the objective lens and thesample.

Further, in the electron microscope in the prior art, even in the casewhere no negative voltage is applied to the sample, if there is a greatpotential difference between the objective lens and the sample, then itis again feared that the electric discharge may occur between theobjective lens and the sample.

Still further, if the voltage applied to the objective lens is set lowerin order to deal with a possible electric discharge to the sample, theelectrons aren't sufficiently energized, resulting in a poor resolution.

An explanation will be further given for a case where the sample to beinspected is a semiconductor wafer having a via, that is a wiringpattern extending in the approximately vertical direction to theupper-layer and lower-layer wiring planes for providing an electricalconnection between the upper layer wiring and the lower layer wiring.

When the semiconductor wafer with the via is inspected for defects byusing a conventional electron microscope, a high voltage, for example, avoltage of 10 kV is applied to the objective lens as in the abovedescription. Further, in this case, it is assumed that the semiconductorwafer is grounded. Accordingly, an electric field is generated betweenthe semiconductor wafer and the objective lens.

These conditions could make the electric field more intense in thevicinity of the via on the surface of the semiconductor wafer, thusforming a high electric field. Then, when the electron beam isirradiated onto the via, a large number of secondary electrons isemitted from the via, which is further accelerated by the high electricfield in the vicinity of the via. Those accelerated secondary electronshave a sufficient energy (>3 eV) to ionize a residual gas generated bythe irradiation of the electron beam onto the semiconductor wafer.Accordingly, the secondary electrons ionize the residual gas so as togenerate ionized charged particles.

Then, said ionized charged particles, i.e., the positive ions, areaccelerated by the high electric field in the vicinity of the via towardthe via to impinge against the via, so that more secondary electrons areemitted from the via. Through a series of these positive feedback,eventually an electric discharge occurs between the objective lens andthe semiconductor wafer and damages the pattern or the like on thesemiconductor wafer, which has been problematic in the prior art.

Thus, an object of the present invention is to provide an electron gunapparatus which can prevent an electric discharge to a sample beinginspected and a method for manufacturing a device by using said electrongun apparatus.

Also, as stated above, an inspection for defects in a mask pattern usedin manufacturing a semiconductor device or in a pattern formed on asemiconductor wafer has been performed by the steps of detectingsecondary electrons emitted from a sample upon irradiation of a primaryelectron beam against a surface of the sample, obtaining a pattern imageof the sample, and comparing said image with a reference image.Typically, such defect inspection apparatus has been equipped with anE×B separator for separating the primary electrons and the secondaryelectrons.

FIG. 52 shows schematically a typical configuration of a projectiveelectron beam inspection apparatus having an E×B separator. An electronbeam emitted from an electron gun 721 is formed to be rectangular inshape with a forming aperture (not shown) and reduced in size by theelectrostatic lenses 722, thus to be a formed beam of 1.25 mm square atthe center of an E×B separator 723. The formed beam is deflected by theE×B separator 723 so as to be normal to a sample W, and reduced to be ⅕in size with an electrostatic lens 722, which is then irradiated againstthe sample W. A beam of the secondary electrons emitted from the sampleW has a certain intensity corresponding to the pattern data on thesample W, which is expanded by the electrostatic lenses 724, 741, andthen enters into a detector 761. The detector 761 generates an imagesignal corresponding to the intensity of the received secondaryelectrons, which is compared with a reference image, thereby detectingany defects in the sample.

The E×B separator 723 has a configuration in which an electric field anda magnetic field cross at right angles within a plane orthogonal to thenormal of the surface of the sample W (the upward direction on paper),so that it advances the electrons straight forward when the relationshipof the electric field, the magnetic field, and the energy and speed ofthe electrons meets certain criteria, while it deflects the electrons inany case other than the said case. In the inspection apparatus of FIG.44, the conditions are set so that the secondary electrons are advancedstraight ahead.

FIG. 53 shows more precisely the movements of the secondary electronsemitted from the rectangular area on the surface of the sample W, whichhas been exposed to the primary electron beam. The secondary electronsemitted from the sample surface are magnified with the electrostaticlens 724, and imaged onto a central area 723 a of the E×B separator 723.Since the electric field and the magnetic field of the E×B separator 723have been set such that the secondary electrons are allowed to beadvanced straight ahead, the secondary electrons are thus advancedstraight ahead to be magnified with the electrostatic lenses 741-1,741-2 and 741-3, and then imaged on a target 761 a within the detector761. Then, the electron in the image is multiplied by MCP (Multi ChannelPlate, not shown) and is formed into an image by a scintillator, CCD(Charge Coupled Device), or the like (not shown). Reference numerals 732and 733 respectively designate aperture diaphragms arranged in asecondary optical system.

FIG. 54 shows a schematic configuration of a conventional E×B separatorand the distribution of an electric field generated by said separator. Apair of parallel plate electrodes 723-1 and 723-2 is used to generate anelectric field, and a pair of magnetic poles 723-3 and 723-4 is used togenerate a magnetic field orthogonal to said electric field. In thisconfiguration, since the magnetic poles 723-3 and 723-4 are made ofmetals having the ground potential, the electric field is forced to bendtoward the ground sides. Accordingly, the distribution of the electricfield is as shown in FIG. 54, and the parallel pattern of the electricfield may only be obtained in the small central region.

In the case where an E×B separator having such a configuration asdescribed above has been applied to a defect inspection apparatus suchas a projective electron beam inspection apparatus, there has been aproblem of efficiency in inspection in that the irradiated region of theelectron beam cannot be enlarged, in order to perform a preciseinspection.

Thus, an another object of the present invention is to provide an E×Bseparator which allows a region including both the electric field andthe magnetic field having uniform intensities and cross at right anglesto each other, to be expanded in a plane parallel to a sample, and whichalso allows the outer diameter of the whole body to be reduced. Further,another object of the present invention is to reduce the aberration forthe detected image obtained, by means of said E×B separator applied to adefect inspection apparatus, thus to conduct the precise defectinspection efficiently.

Also, as stated above, there is a conventional apparatus which, in aninspection of a pattern on a semiconductor wafer or a photo mask with anelectron beam, reveals a defect in the following way: primarily it scansthe surface of a sample such as the semiconductor wafer or the photomask, or it scans the sample, by sending the electron beam thereto;secondarily it detects secondary charged particles generated from thesurface of said sample to generate image data based on the detectedresult; and lastly it compares the data per cell or die.

However, the above defect inspection apparatus in the prior art has beenproblematic in that the irradiation of the electron beam causes thesurface of the sample to be charged, and carriers from this chargingcause a distortion in the image data, which makes it difficult to detectany defects accurately. When alternatively the electron beam current isreduced to make the distortion by the carriers small enough to resolvethe problem of said distortion in the image data, the S/N ratio for thesecondary electron signal is adversely affected, so that the possibilityof invalid error detection is increased, which has been another problem.Further, it has also been a problem in the prior art that multiplescanning and averaging processes for improving the S/N ratio causes adecrease in throughput.

Therefore, another object of the present invention is to provide anapparatus which prevents any distortion from being caused by charging,or which minimizes such distortions if any, and thereby allows a highlyaccurate defect inspection to be performed, and also to provide a methodfor manufacturing a device by using said apparatus.

Also, there has been known an apparatus for inspecting a substrate forany defects in an image formed on the substrate in such a manner thatthe apparatus irradiates a charged particle beam against a surface ofthe substrate to scan said surface by said charged particle beam,detects secondary electrons emanated from the surface of the substrate,generates image data from the detected result, and then compares thedata for each die to one another to detect those defects.

However, this type of imaging apparatus according to the prior art,including the above-described apparatus that has been disclosed in thepublication, has been problematic in that the potential distribution onthe surface of the substrate or the object to be inspected is notnecessarily uniform and the contrast of the image is insufficient, whichmay cause distortion.

Therefore, a further object of the present invention is to provide animaging apparatus having an improved performance in defect detectionwithout any loss of throughput.

Another object of the present invention is to provide an imagingapparatus having an improved performance in defect detection byimproving the contrast in an image obtained by the detection ofsecondary electrons from the object to be inspected.

Still another object of the present invention is to provide an imagingapparatus having improved performance in defect detection by makinguniform the potential distribution on the surface of an object to beinspected and thereby improving the contrast, thus reducing distortion,in an image obtained by the detection of secondary electrons from saidsurface of the object to be inspected.

Yet another object of the present invention is to provide a devicemanufacturing method in which a sample in the course of processes isevaluated by using such an imaging apparatus as described above.

There has also been one such prior art defect inspection apparatus usedconventionally in a semiconductor manufacturing process or the like,which inspects a sample such as a wafer or the like for any defects bydetecting secondary electrons emanated by irradiating a primary electronbeam onto the sample.

Japanese patent Application Public Disclosure No.11-132975, for example,discloses a defect inspection apparatus which comprises: an electronbeam irradiating section for irradiating an electron beam against asample; a projecting optical section for image-forming a one-dimensionaland/or a two-dimensional image of secondary or reflected electrons, saidsecondary electrons being emanated in response to shape, material, andvariation in potential on the surface of the sample; an electron beamdetecting section for outputting a detection signal based on a formedimage; an image display section for receiving said detection signal anddisplaying an electron image of the surface of the sample based thereon;and an electron beam deflecting section for changing the angle ofincidence of the electron beam irradiated from the electron beamirradiating section onto the sample and the angle of intake of thesecondary or reflected electrons into the projecting optical section.According to this inspection apparatus, the primary electron beam isirradiated onto a surface in a specified rectangular region of thesample wafer of the real device.

However, if the electron beam is irradiated on the surface in arelatively large area of the sample wafer of the real device, due to thesample surface being made of an insulating material such as silicondioxide or silicon nitride, the electron beam irradiation against thesample surface and associated emanation of secondary electrons from thesample surface causes the sample surface to be positively charged, andan electric field produced by this potential has problematically causeda variety of image disorders in the secondary electron beam image.

The present invention has been made in the light of above-mentionedfacts, and an object thereof is to provide an defect inspectionapparatus and a defect inspection method that enable an inspection of asample to be performed with higher accuracy by reducing positive chargebuiled-up in the surface of the sample, thereby overcoming the problemof disorder associated with this charge-up.

Another object of the present invention is to provide a semiconductormanufacturing method that can improve the yield of devices and preventdelivery of any defective products to market by using an inspectionapparatus described above to carry out a defect inspection of a sample.

Further, a stage for accurately positioning a sample in a vacuumatmosphere has been used in an apparatus in which a charged particlesbeam such as an electron beam is irradiated onto the surface of a samplesuch as a semiconductor wafer so as to expose the surface of the sampleto a pattern of a semiconductor circuit or the like, or so as to inspecta pattern formed on the surface of the sample, or in another apparatusin which the charged particles beam is irradiated onto the sample so asto apply an ultra-precise processing thereto.

When said stage is required to be positioned highly accurately, onestructure has been conventionally employed, in which the stage issupported in non-contact manner by a hydrostatic bearing. In this case,the vacuum level in a vacuum chamber is maintained by forming adifferential exhausting mechanism for exhausting a high pressure gas inan area of the hydrostatic bearing so that the high pressure gassupplied from the hydrostatic bearing may not be directly exhausted intothe vacuum chamber.

FIG. 55 shows one of the examples of such a stage according to the priorart. In the configuration of FIG. 55, the tip portion of an opticalcolumn 71 or a charged particles beam irradiating section 72 of acharged particles beam apparatus for emitting and irradiating a chargedparticles beam against a sample is attached to a housing 98 which makesup a vacuum chamber C. The interior of the optical column is exhaustedto vacuum through a vacuum pipe 710, as in the chamber C through avacuum pipe 911. Herein, the charged particles beam is irradiated fromthe tip portion 72 of the optical column 71 against a sample W such as awafer or the like placed thereunder.

The sample W is detachably held on a sample table 94, and the sampletable 94 is mounted on the upper face of a Y directionally movable unit95 of an XY stage (hereafter referred to as a stage for simplicity). Theabove Y directionally movable unit 95 is equipped with a plurality ofhydrostatic bearings 90 attached on planes (on both of the right andleft faces and also on a bottom face in FIG. 55[A]) facing to guideplanes 96 a of an X directionally movable unit 96 of the stage 93, andis allowed to move in the Y direction (lateral direction in FIG. 55[B])with a micro gap maintained between the guide planes and itself by saidhydrostatic bearings 90. Further, a differential exhausting mechanism isprovided surrounding the hydrostatic bearing so that a high-pressure gassupplied to the hydrostatic bearing does not leak into the vacuumchamber C. This is shown in FIG. 56. Doubled grooves 918 and 917 areformed surrounding the hydrostatic bearings 90, and are regularlyexhausted to vacuum through a vacuum pipe by a vacuum pump (not shown).Owing to such structure, the Y directionally movable unit 95 is allowedto move freely in the Y direction in the vacuum atmosphere as supportedin the non-contact manner. Those doubled grooves 918 and 917 are formedin a plane of the movable unit 95 in which the hydrostatic bearing 90 isarranged, so as to circumscribe said hydrostatic bearing. The structureof the hydrostatic bearing may be any of those conventionally known andits detailed explanation can be omitted here.

The X directionally movable unit 96 having said Y directionally movableunit 95 loaded thereon is formed to be concave in shape with the topface opened, as obviously seen from FIG. 55, and said X directionallymovable unit 95 is also provided with completely similar hydrostaticbearings and grooves, and further the unit 96 is supported in anon-contact manner with respect to the stage 97 so as to be movablefreely in the X direction.

Combining said Y directionally movable unit 95 with the X directionallymovable unit 96 allows the sample W to be moved to a desired position inthe horizontal direction relative to the tip portion of the opticalcolumn or the charged particles beam irradiating section 72, so that thecharged particles beam can be irradiated to a desired location of thesample.

With the stage including a combination of the hydrostatic bearing andthe differential exhausting mechanism as described above, the guideplane 96 a or 97 a facing the hydrostatic bearing 90 makes areciprocating motion between a high-pressure atmosphere in theelectrostatic bearing portion and a vacuum environment within thechamber while the stage moves. During this reciprocating motion, suchgas supply cycle is repeated in which while the guide plane is exposedto the high-pressure atmosphere, the gas is adsorbed onto the guideplane, and upon being exposed to the vacuum environment, the adsorbedgas is desorbed into the environment. Because of this gas supply cycle,every time when the stage moves, it has happened that the vacuum levelin the chamber C is lowered, which has caused such problems that theexposure, inspection, or processing with the charged particles beamdescribed above could not be carried out stably, and the sample might becontaminated.

Therefore, an another object of the present invention is to provide acharged particles beam apparatus capable of preventing the degradationof the vacuum level and thereby allow a process such as inspection orprocessing by a charged particles beam to be carried out stably.

Another object of the present invention is to provide a chargedparticles beam apparatus having a non-contact supporting mechanism bymeans of a hydrostatic bearing and a vacuum sealing mechanism by meansof a differential exhausting so as to produce a pressure differencebetween the charged particles beam irradiating region and a supportingsection of the hydrostatic bearing.

Still another object of the present invention is to provide a chargedparticles beam apparatus capable of reducing a gas desorbed from thesurface of a part facing to the hydrostatic bearing.

Still another object of the present invention is to provide a defectinspection apparatus for inspecting the surface of a sample or anexposure apparatus for delineating a pattern on a surface of a sample,by using such a charged particles beam apparatus as described above.

Yet another object of the present invention is to provide asemiconductor manufacturing method for manufacturing a semiconductordevice by using a charged particles beam apparatus such as describedabove.

Also, in the conventional stage including a combination of thehydrostatic bearing and the differential exhausting mechanism shown inFIG. 55, there have been such problems that because of the differentialexhausting mechanism having been added, the structure has become morecomplicated and its reliability as a stage has decreased while its costhas increased over that of a stage having a hydrostatic bearing used inthe atmospheric pressure.

Therefore, another object of the present invention is to provide acharged particles beam apparatus having a simple structure capable ofbeing made compact without employing a differential exhausting mechanismfor the XY stage.

Another object of the present invention is to provide a chargedparticles beam apparatus with a differential exhausting mechanism forexhausting a region on a surface of a sample to which a chargedparticles beam is to be irradiated, as well as for exhausting the insideof a housing containing an XY stage to vacuum.

Still another object of the present invention is to provide a defectinspection apparatus for inspecting the surface of a sample for defectsor an exposing apparatus for delineating a pattern on the surface of thesample by using either of the charged particles beam apparatusesdescribed above.

Yet another object of the present invention is to provide a method formanufacturing a semiconductor device by using either of the chargedparticles beam apparatuses described above.

Also, as stated above, there has been used in the semiconductormanufacturing processes or the like a defect inspection apparatus forinspecting a sample such as a semiconductor wafer for defects bydetecting secondary electrons emitted upon an irradiation of a primaryelectrons against said sample.

In such defect inspection apparatus, there has been employed atechnology in which an image recognition technique is put into practicaluse to accomplish an automated inspection and to achieve higherefficiency in the inspection. In this technology, a computer carries outa matching operation between pattern image data for a region to beinspected in the sample surface obtained by detecting the secondaryelectrons and reference image data for the sample surface stored inadvance, so that it is automatically determined if there are any defectsexisting in the sample, based on the operation results.

Recently, especially in the semiconductor manufacturing field, patternsare increasingly miniaturized, and consequently requiring detection offiner defects with high precision and efficiency. Under such condition,even the defect inspection apparatus taking advantage of the imagerecognition technique described above must further improve itsrecognition accuracy.

However, there has been such a problem associated with the prior artdescribed above, which is that a position mismatch occurs between theimage of the secondary electron beam obtained upon irradiating theprimary electron beam against the region to be inspected in the samplesurface and the reference image prepared in advance, which decreases theaccuracy in defect detection. This position mismatch becomes a seriousproblem especially when the irradiation region of the primary electronbeam is offset to the wafer resulting in the inspection patternpartially being out of the detection image of the secondary electronbeam, which could not be handled only with the technology for optimizinga matching region within the detection image. This problem could be afatal drawback especially in the inspecting of patterns of highprecision.

Therefore, a still further object of the present invention is to providea defect inspection apparatus which can prevent a loss of accuracy inthe defect detection possibly caused by a position mismatch between theimage of an inspection sample and a reference image.

Another object of the present invention is to provide a semiconductormanufacturing method used in semiconductor device manufacturingprocesses, which attempts to improve the yield of devices and to preventany faulty products from being delivered to market by using a defectinspection apparatus as described above for performing a defectdetection of a sample.

Means to Solve the Problem

The present invention has employed a method referred to as a projectingmethod using an electron beam as a means for improving the inspectionrate which has been essential drawback of the SEM method. The projectingmethod will now be described below.

In the projecting method, an observation region on a sample isirradiated in block by a primary electron beam (i.e., no scanning but anirradiation covering a certain area), and secondary electrons emanatedfrom the irradiated region are formed into an image in block by a lenssystem on a detector (a micro-channel plate plus fluorescent screen) asan image of electron beam. That image is used in a two-dimensional CCD(charge coupled device) or a TDI-CCD (a line image sensor) to convertthe image data into an electric signal, which is then output onto a CRTor stored in some storage medium. From this image data, defects in thesample wafer (the semiconductor (Si) wafer being processed) may bedetected. In the case of the CCD, the moving direction of the stageextends along the shorter axis (it may be along the longer axis), andthe movement is made by the step and repeat manner. As for the stagemovement in the case of TDI-CCD, the stage is continuously moved in theaccumulation direction. Since the TDI-CCD allows the image to beserially obtained, the TDI-CCD may be used when the defect inspectionsare to be continuously carried out. The resolution is determineddepending on the magnification and accuracy of an image-forming opticalsystem (a secondary optical system), and in an embodiment, a resolutionof 0.05 μm has been obtained. In this example, with a resolution of 0.1μm and the electron beam irradiation condition of 1.6 μA for the area of200 μm×50 μm, an inspection time of about one hour per 20 cm wafer hasbeen accomplished, which is 8 times higher than in the SEM method. Thespecification of the TDI-CCD employed herein has 2048 pixels×512 arrayswith a line rate of 3.3 μs (at line frequency of 300 kHz). In thisexample, although an irradiation area is determined so as to conform tothe specification of the TDI-CCD employed, the irradiation area may bechanged depending on the object to be irradiated.

Problems in this projecting method are; (1) a charge build-up is morelikely to occur in the surface of a sample due to an in-blockirradiation of electron beam; and (2) an electron current obtained bythis method is limited (up to about 1.6 μA), which prohibits anyimprovement in inspection rate.

Now, in order to dissolve the above mentioned problems of theconventional techniques, according to 1^(st) aspect of the presentinvention, there is provided an inspection apparatus for inspecting anobject to be inspected by irradiating either of a charged particles oran electromagnetic waves onto said object, said apparatus comprising:

a working chamber for inspecting said object, said chamber capable ofbeing controlled to be vacuum atmosphere;

a beam generating means for generating either of said charged particlesor said electromagnetic waves as a beam;

an electronic optical system for guiding and irradiating said beam ontosaid object to be inspected held in said working chamber, detecting asecondary charged particles emanated from said object to be inspectedand introducing said secondary charged particles to an image processingsystem;

said image processing system for forming an image by said secondarycharged particles;

an information processing system for displaying and/or storing thestatus information of said object to be inspected based on output fromsaid image processing system; and

a stage unit for operatively holding said object to be inspected so asto be movable with respect to said beam.

According to 2^(nd) aspect of the present invention, in the inspectionapparatus of 1^(st) aspect, the inspection apparatus further comprises acarrying mechanism for securely accommodating said object to beinspected and for transferring said object to or from said workingchamber.

According to 3^(rd) aspect of the present invention, in the inspectionapparatus of 2^(nd) aspect, said carrying mechanism comprises;

a mini-environment chamber for supplying a clean gas to said object tobe inspected to prevent dust from contacting said object to beinspected;

at least two loading chambers disposed between said mini-environmentchamber and said working chamber, and adapted to be independentlycontrollable so as to be a vacuum atmosphere; and

a loader having a carrier unit capable of transferring said object to beinspected between said mini-environment chamber and said loadingchambers, and another carrier unit capable of transferring said objectto be inspected between said one loading chamber and said stage device;

wherein said working chamber and said loading chamber are supportedthrough a vibration isolator.

According to 4^(th) aspect of the present invention, in the inspectionapparatus of 1^(st) aspect, said inspection apparatus furthercomprising:

a precharge unit for irradiating a charged particle beam to said objectto be inspected placed in said working chamber to reduce variations incharge on said object to be inspected; and

a potential applying mechanism for applying a potential to said objectto be inspected.

According to 5^(th) aspect of the present invention, in the inspectionapparatus of 3^(rd) aspect, said loader includes:

a first loading chamber and a second loading chamber capable ofindependently controlling an atmosphere therein;

a first carrier unit for carrying said object to be inspected betweensaid first loading chamber and the outside of said first loadingchamber; and

a second carrier unit disposed in said second loading chamber forcarrying said object to be inspected between said first loading chamberand said stage device.

According to 6^(th) aspect of the present invention, in the inspectionapparatus of 1^(st), 2^(nd) or 3^(rd) aspect, the inspection apparatusfurther comprises:

an alignment controller for observing the surface of said object to beinspected for an alignment of said object to be inspected with respectto said electron-optical system to control the alignment; and

a laser interference range finder for detecting coordinates of saidobject to be inspected on said stage device, said coordinates of saidobject to be inspected being determined by said alignment controllerusing patterns formed on said object to be inspected.

According to 7^(th) aspect of the present invention, in the inspectionapparatus of 1^(st), 2^(nd) or 3^(rd) aspect, the alignment of saidobject to be inspected includes:

rough alignment performed within said mini-environment space; and

alignment in XY-directions and alignment in a rotating directionperformed on said stage device.

According to 8^(th) aspect of the present invention, in the inspectionapparatus of 1^(st), 2^(nd) or 3^(rd) aspect, said electron opticalsystem includes:

an E×B separator for deflecting said secondary charged particle towardsaid detector by a field where an electric field and a magnetic fieldcross at right angles; and an electrode for controlling an electricfield intensity in a plane of said sample to be inspected, said planebeing exposed to said electron beam irradiation, said electrode beingarranged between said objective lens and said sample to be inspected andhaving a shape approximately symmetrical with respect to the opticalaxis of irradiation of said beam.

According to 9^(th) aspect of the present invention, in the inspectionapparatus of 1^(st), 2^(nd) or 3^(rd) aspect, said apparatus includes anE×B separator, to which said charged particle and said secondary chargedparticle are entered, said secondary charged particle being advanced inthe direction approximately opposite to said charged particle, and inwhich said charged particle or said secondary charged particle isdeflected selectively, said E×B separator characterized in that: anelectrode for generating an electric field is made up of three or morepairs of non-magnetic conductive electrodes, and is arranged so as toapproximately form a cylinder.

According to 10^(th) aspect of the present invention, in the inspectionapparatus of 1^(st), 2^(nd) or 3^(rd) aspect, said apparatus furthercomprises a charged particle irradiating section for irradiating chargedparticles in advance against said inspecting region just before theinspection.

According to 11^(th) aspect of the present invention, in the inspectionapparatus of 1^(st), 2^(nd) or 3^(rd) aspect, said apparatus furthercomprising a means for making the distribution uniform or reducing thepotential level of electric charge residing on said object.

According to 12^(th) aspect of the present invention, in the inspectionapparatus of 1^(st), 2^(nd) or 3^(rd) aspect, electrons having energylower than that of said charged particles are supplied to said sample atleast during said detector detecting said secondary charged particleimage.

According to 13^(th) aspect of the present invention, in the inspectionapparatus of 1^(st), 2^(nd) or 3^(rd) aspect, said stage is an XY stage,which is accommodated in a working chamber and supported by ahydrostatic bearing in a non-contact manner with respect to said workingchamber;

said working chamber in which said stage is accommodated is exhausted tovacuum; and

a differential exhausting mechanism is arranged surrounding a portion insaid charged particle beam apparatus, where the charged particle beam isto be irradiated against a surface of said sample, so that a region onsaid sample to which said charged particle beam is to be irradiated maybe exhausted to vacuum.

According to 14^(th) aspect of the present invention, in the inspectionapparatus of 1^(st), 2^(nd) or 3^(rd) aspect, said apparatus includes anapparatus for irradiating a charged particle beam against a surface of asample loaded on an XY stage while moving said sample to a desiredposition in a vacuum atmosphere,

said XY stage is provided with a non-contact supporting mechanism bymeans of a hydrostatic bearing and a vacuum sealing mechanism by meansof differential exhausting, and a divider is provided for making theconductance smaller between a charged particle beam irradiating regionand a hydrostatic bearing support section, so that there is a pressuredifference to be produced between said charged particle beam irradiatingregion and said hydrostatic bearing support section.

According to 15^(th) aspect of the present invention, in the inspectionapparatus of 1^(st), 2^(nd) or 3^(rd) aspect, said apparatus includes;

an image obtaining means for obtaining respective images for a pluralityof regions to be inspected, said regions being displaced from oneanother while being partially superimposed one on another on saidsample;

a storage means for storing a reference image; and a defectdetermination means for determining any defects in said sample bycomparing said respective images obtained by said image obtaining meansfor said plurality of regions to be inspected with said reference imagesstored in said storage means.

According to 16^(th) aspect of the present invention, there is provideda device manufacturing method, which comprises the step of:

detecting defects on a wafer using an inspection apparatus according toanyone of 1^(st) to 15^(th) aspect in the middle of a process orsubsequent to the process.

According to 1^(st) to 16^(th) aspects of the present invention, thefollowing advantages are provided:

(A) the general configuration can be established for an inspectionapparatus in accordance with a charged particle based projection scheme,which can process objects under inspecting at a high throughput;

(B) a clean gas is forced to flow to an object to be inspected withinthe mini-environment space to prevent dust from attaching to the objectto be inspected, and a sensor is provided for observing the cleanliness,thereby making it possible to inspect the object to be inspected whilemonitoring dust within the space;

(C) when the loading chamber and the working chamber are integrallysupported through a vibration isolator, an object to be inspected can becarried to the stage device and inspected thereon without being affectedby the external environment; and

(D) when the precharge unit is provided, a wafer made of an insulatingmaterial will not be affected by charging.

According to 17^(th) aspect of the present invention, there is providedan inspection apparatus which comprises:

a beam source for irradiating a charged particle against a sample to beinspected;

a retarding-field type objective lens for decelerating said chargedparticle as well as for accelerating secondary charged particlegenerated by said electron beam irradiated against said sample to beinspected;

a detector for detecting said secondary charged particle;

an E×B deflecting system for deflecting said secondary charged particletoward said detector by a field where an electric field and a magneticfield cross at right angles; and

an electrode for controlling the electric field intensity in a plane ofsaid sample to be inspected, said plane being exposed to said chargedparticle irradiation, said electrode being arranged between saidretarding-field type objective lens and said sample to be inspected andhaving a shape approximately symmetrical with respect to an optical axisof irradiation of said charged particles.

According to 18^(th) aspect of the present invention, in the electronbeam apparatus of 17^(th) aspect, a voltage applied to said electrode iscontrolled in order to control said electric field intensity dependingon a category of said sample to be inspected.

According to 19^(th) aspect of the present invention, in the electronbeam apparatus of 17^(th) aspect, said sample to be inspected is asemiconductor wafer, and said voltage applied to said electrode in orderto control said electric field intensity is controlled depending onwhether or not said semiconductor device has a via.

According to 20^(th) aspect of the present invention, there is provideda device manufacturing method which uses an electron beam apparatusdefined by either of 17^(th) to 19^(th) aspect, wherein said method ischaracterized in that a semiconductor wafer, which has been prepared assaid sample to be inspected, is inspected for defects by using saidinspecting apparatus in a manufacturing process of the device orsubsequent to the process.

According to 17^(th) to 20^(th) aspect of the present invention, thefollowing advantages are provided.

Since the electrode having a shape approximately symmetrical withrespect to the axis of irradiation of the charged particles has beenarranged between the sample to be inspected and the objective lens so asto control the electric field intensity in the charged particleirradiated plane of the sample to be inspected, therefore the electricfield between the sample to be inspected and the objective lens can becontrolled.

Further, since the electrode having a shape approximately symmetricalwith respect to the axis of irradiation of the charged particle has beenarranged between the sample to be inspected and the objective lens so asto weaken the electric field intensity in the charged particleirradiated plane of the sample to be inspected, therefore the electricdischarge between the sample to be inspected and the objective lens canbe eliminated.

Since there has been no modification such as decreasing the voltageapplied to the objective lens and therefore the secondary chargedparticles can go through the objective lens efficiently, thus adetection efficiency can be improved and a signal with good S/N ratiocan be obtained.

Further, the voltage can be controlled so as to weaken the electricfield intensity in the charged particle irradiated plane of the sampleto be inspected, depending on the type of sample to be inspected.

For example, if the sample to be inspected is of a type that is likelyto cause an electric discharge between the objective lens and itself,the electric discharge can be prevented by weakening the electric fieldintensity in the charged particle irradiated plane of the sample to beinspected by changing the voltage applied to the electrode.

Further, the voltage applied to the electrode can be changed dependingon whether or not said semiconductor device has a via, that is, thevoltage applied in order to weaken the electric field intensity in thecharged particle irradiated plane of the semiconductor wafer can bechanged.

For example, if the sample to be inspected is of a type that is likelyto cause an electric discharge between the objective lens and itself,the electric discharge especially in the via or in the vicinity of thevia can be prevented by changing the electric field caused by theelectrodes and thereby weakening the electric field intensity in thecharged particle irradiated plane of the sample to be inspected.

Further, since an electric discharge is prevented between the via andthe objective lens, there would be no damage to the pattern or the likein the semiconductor wafer, which otherwise would be caused by theelectric discharge.

Further, since the potential applied to the electrode has been madelower than that applied to the sample to be inspected, therefore theelectric field intensity in the charged particle irradiated plane of thesample to be inspected can be weakened, thus preventing the electricdischarge to the sample to be inspected.

Yet further, since the potential applied to said electrode is negativeand the sample to be inspected has been grounded, the electric fieldintensity is weakened in the charged particle irradiated plane of thesample to be inspected, to prevent an electric discharge to the sampleto be inspected.

According to 21^(st) aspect of the present invention, there is providedan E×B separator, into which a first charged particle beam and a secondcharged particle beam enter, said second charged particles beingadvanced in the direction approximately opposite to said first chargedparticle beam, and in which said first charged particle beam or saidsecond charged particle beam is deflected selectively, said E×Bseparator characterized in that:

an electrode for generating an electric field is made up of three ormore pairs of non-magnetic conductive electrodes, and is arranged so asto form cylinder.

According to 22^(nd) aspect of the present invention, in the E×Bseparator of 21^(st) aspect, each of a pair of parallel plate magneticpoles for generating a magnetic field is respectively arranged outsideof said cylinder composed of said three or more pairs of non-magneticconductive electrodes, and projections are formed in peripheral portionsof the opposite face of each of said pair of parallel plate magneticpoles.

According to 23^(rd) aspect of the present invention, in the E×Bseparator of 22^(nd) aspect, in a passage space of lines of magneticforce of the magnetic field generated, a majority of the passage spaceother than that between said parallel plate magnetic poles is formed tobe cylindrical shape coaxial with said cylinder composed of said threeor more pairs of non-magnetic conductive electrodes.

According to 24^(th) aspect of the present invention, in the E×Bseparator of 22^(nd) or 23^(rd) aspect, said parallel plate magneticpoles are made of permanent magnets.

According to 25^(th) aspect of the present invention, in the defectinspection apparatus using the E×B separator defined by either of21^(st) to 24^(th) aspect, either one of said first charged particlebeam or said second charged particle beam is a primary charged particlebeam to be irradiated against a sample to be inspected, and the other isa secondary charged particle beam generated from said sample by theirradiation of said primary charged particle beam.

According to 21^(st) to 25^(th) aspect of the present invention, thefollowing advantages are provided.

Both of the electric field and the magnetic field are allowed to emergeuniformly in the larger region around the optical axis, so that even ifthe area exposed to the irradiation of the charged particle is extended,the aberration for the image passed through the E×B separator would fallinto a reasonable range of values.

Since the projections have been arranged in the peripheral portions ofthe magnetic poles generating the magnetic field, and said magneticpoles are also arranged outside of the electrodes for generating theelectric field, they allow a uniform magnetic field to be generated,reducing a distortion by the magnetic poles. Further, since the magneticfield has been generated by use of the permanent magnets, the E×Bseparator can be fully installed in vacuum. Still further, theelectrodes for generating the electric field and the magnetic circuitfor forming the magnetic path have been formed into coaxial cylindricalshapes centered to the optical axis, which makes it possible to reducein size the E×B separator as a whole.

According to 26^(th) aspect of the present invention, there is provideda projective type electron beam inspection apparatus, which comprises acharged particle irradiating section, a lens system, a deflectingsystem, an E×B filter (Wiener filter), and a secondary charged particledetector, in which charged particles from said charged particleirradiating section is irradiated onto an inspecting region of a samplethrough said lens system, said deflecting system, and said E×B filter,and secondary charged particles emitted from the sample are formed intoan image in said secondary charged particle detector by said lenssystem, said deflecting system, and said E×B filter, and an electricsignal thereof is inspected as the image, said apparatus characterizedin further comprising a charged particle irradiating section forirradiating charged particles in advance against said inspecting regionjust before the inspection.

According to 27^(th) aspect of the present invention, in the apparatusof 26^(th) aspect, said charged particle is selected from the groupconsisting of electron, positive or negative ion, or plasma.

According to 28^(th) aspect of the present invention, in the apparatusof 26^(th) or 27^(th) aspect, the energy of said charged particles isequal to or less than 100 eV.

According to 29^(th) aspect of the present invention, in the apparatusof 26^(th) or 27^(th) aspect, the energy of said charged particles isnot greater than 30 eV.

According to 30^(th) aspect of the present invention, there is provideda device manufacturing method using an inspection apparatus defined byeither of 26^(th) to 29^(th) aspect, wherein a pattern inspection isperformed in the device manufacturing processes.

According to 26^(th) to 30^(th) aspect of the present invention, thefollowing advantages are provided.

Since a pre-treatment by means of a charged particle irradiation isemployed just before a measurement, an evaluated image distortion by thecharging would not occur or could be neglible, therefore all defects canbe accurately detected.

Further, since a high current can be used for scanning a stage by suchan amount that has caused a problem in the prior art, a large amount ofsecondary electrons can be detected and a detection signal having a goodS/N ratio can be obtained, thus reliability of the defect detection.

Still further, with a larger S/N ratio, faster scanning of the stage canstill produce good image data, thus improving inspection throughput.

According to 31^(st) aspect of the present invention, there is providedan imaging apparatus which irradiates a charged particle beam emittedfrom a beam source against an object and detects a secondary chargedparticle emanated from the object by using a detector so as to collectan image data of said object, to inspect the object for defects and soforth,

said apparatus characterized in further comprising a means for makingthe distribution uniformor reducing the potential level of electriccharge residing on said object.

According to 32^(nd) aspect of the present invention, in the imagingapparatus of 31^(st) aspect, said means comprises an electrode disposedbetween said beam source and said object so as to be capable ofcontrolling said electric charge.

According to 33^(rd) aspect of the present invention, in the imagingapparatus of 31^(st) aspect, said means is designed so as to operateduring the idle time between measurement timings.

According to 34^(th) aspect of the present invention, in the imagingapparatus of 31^(st) aspect, said imaging apparatus further comprises:

at least one or more primary optical systems for irradiating a pluralityof charged particle beams against said object; and

at least one or more secondary optical systems for guiding electronsemanating from said object to at least one or more detectors, wherein

each of said plurality of primary charged particle beams is respectivelyirradiated onto a spot such that the distance between any two spots isgreater than the distance resolution of said secondary optical system.

According to 35^(th) aspect of the present invention, there is provideda device manufacturing method characterized in that a defect in a waferis detected in the course of processing by using the imaging apparatusdisclosed in either of 31^(st) to 34^(th) aspects.

According to the invention of 31^(st) to 35^(th) aspects, the followingeffects may be expected to obtain.

(A) Distortion in an image caused by electric charging may be reducedregardless of the properties of the object to be inspected.

(B) Since the idle time between the timings for the conventionalmeasurement is used to offset the electric charging and make it uniform,there would be no affect on throughput.

(C) Since real-time processing becomes possible, time for anypost-processing, a memory and the like are no more necessary.

(D) A fast and highly accurate observation of an image and detection ofa defect may be accomplished.

According to 36^(th) aspect of the present invention, there is providedan inspection apparatus for inspecting a sample for defects, comprising:a charged particle irradiation means capable of irradiating primarycharged particles against said sample; a projecting means for projectingsecondary charged particles emanating from said sample by theirradiation of said primary charged particles so as to form an image; adetection means for detecting an image formed by said projecting meansas an electron image of said sample; and a defect evaluation means fordetermining a defect in said sample based on an electron image detectedby said detection means, said apparatus characterized in that electronshaving energy lower than that of said irradiated primary chargedparticle are supplied to said sample at least during said detectionmeans detecting said electron image.

In the 36^(th) aspect of the present invention, the charged particleirradiation means irradiates primary charged particles against thesample, and the projecting means projects the secondary charged particleemanating from the sample in response to the irradiation of the primarycharged particles so as to form the image in the detection means. Thesample, which has emitted out the secondary charged particle therefrom,is charged up to a positive potential. The detection means detects theformed image as the electron image of the sample, and the defectevaluation means determines whether any defects exist in the samplebased on the detected electron image. In that case, at least during thetime period when the detection means is detecting the electron image,electrons having energy lower than that of the irradiated primarycharged particles is supplied to the sample. Those electrons of lowerenergy may neutralize the sample that has been positively charged-up byan emanation of the secondary charged particle gone from the sample.This allows the secondary charged particle to be formed into an imagewithout any substantial effect from the positive potential of thesample, and thereby the detection means can detect the electron imagewith the reduced image distortion.

As for electrons having energy lower than that of the primary chargedparticle, preferably, for example, UV photoelectrons may be used. The UVphotoelectron is defined as an electron emanated from a substance suchas metal or the like by the photoelectric effect upon irradiation of abeam of light including ultra-violet ray (UV) to said substance.Alternatively, any means other than the charged particle irradiationmeans, for example, an electron gun or the like may be used to generateelectrons having the energy lower than that of the primary chargedparticle.

It is to be noted that those secondary charged particles which haveemanated from the sample by the irradiation of the primary chargedparticles may include some reflected electrons generated by the primarycharged particle which have been reflected from the sample surface inaddition to the secondary electrons originated from those electronswhich were once in the sample but which have emanated from the surfacethereof by the impingement of the primary charged particle thereto. Itis apparent that the electron image to be formed by the detection meansof the present invention also includes a contribution from those backscattered electrons.

According to 37^(th) aspect of the present invention, there is provideda defect inspection apparatus for inspecting a sample for any defects,comprising: a charged particle irradiation means capable of irradiatinga primary charged particle against said sample; a projecting means forprojecting a secondary charged particle emanated from said sample by theirradiation of said primary charged particle so as to form an image; adetection means for detecting an image formed by said projecting meansas an electron image of said sample; and a defect evaluation means fordetermining a defect in said sample based on the electron image detectedby said detection means, said apparatus characterized in furthercomprising a UV photoelectron supply means capable of supplying a UVphotoelectron to said sample.

In the 37^(th) aspect of the present invention, so far as the reductionin image disorder can be accomplished effectively according to thepresent invention by the UV photoelectron supply means (or in the UVphotoelectron supply), the low energy electrons can be supplied to thesample with arbitrary timing and for arbitrary duration. For example,the supply of UV photoelectrons may be started before the primarycharged particles are irradiated, before the secondary charged particlesare formed into an image, or after the secondary charged particles havebeen formed into an image but before the electron image is detected.Further, as in the first aspect, the UV photoelectron supply maycontinue at least while the secondary charged particle is beingdetected, but the supply of UV photoelectrons may be stopped even beforeor during the electron image detection if the sample has beenelectrically neutralized sufficiently.

According to 38^(th) aspect of the present invention, there is provideda defect inspection method for inspecting a sample for any defects,which comprises: an irradiating process for irradiating primary chargedparticles against said sample; a projecting process for projectingsecondary charged particles emanated from said sample by the irradiationof said primary charged particle so as to form an image; a detectingprocess for detecting said image formed in said projecting process as anelectron image of said sample; and a defect evaluating process fordetermining a defect in said sample based on said electron imagedetected in said detecting process, wherein electrons having energylower than that of said primary charged particles are supplied to saidsample at least during said electron image being detected in saiddetecting process.

According to 39^(th) aspect of the present invention, there is provideda defect inspection method for inspecting a sample for any defects,which comprises: an irradiating process for irradiating primary chargedparticles against said sample; a projecting process for projectingsecondary charged particles emanated from said sample by the irradiationof said primary charged particles so as to form an image; a detectingprocess for detecting said image formed in said projecting process as anelectron image of said sample; and a defect evaluating process fordetermining a defect in said sample based on said electron imagedetected in said detecting process, said method further comprising: a UVphotoelectron supplying process for supplying said sample with UVphotoelectrons.

According to 40^(th) aspect of the present invention, there is provideda semiconductor manufacturing method which includes a process forinspecting for any defects a sample to be required in manufacturing asemiconductor device by using a defect inspection apparatus of 36^(th)or 37^(th) aspect.

According to the invention of 36^(th) to 40^(th) aspects, the followingadvantages can be expected.

Since electrons having energy lower than that of the primary chargedparticles are supplied to the sample to be inspected, positive charge-upof the surface of the sample possibly caused by the secondary chargedparticle emanation may be reduced, and thereby an image distortion ofthe secondary charged particle resulting from the charging may be alsoresolved, and the sample may be inspected for defects with highaccuracy.

Further, when the defect inspection is conducted by using such a defectinspection apparatus as described above, the yield of the product can beimproved and the delivery of defective products can also be prevented.

According to 41^(st) aspect of the present invention, there is providedan apparatus for irradiating a charged particle beam against the surfaceof a sample loaded on an XY stage while moving said sample to a desiredposition in vacuum atmosphere, said apparatus characterized in that:

said XY stage is provided with a non-contact supporting mechanism bymeans of a hydrostatic bearing and a vacuum sealing mechanism by meansof differential exhausting, and

a divider is provided for reducing the conductance between the chargedparticle beam irradiating region and a hydrostatic bearing supportsection, so that there is a pressure difference produced between saidcharged particle beam irradiating region and said hydrostatic bearingsupport section.

According to 42^(nd) aspect of the present invention, in the chargedparticle beam apparatus of 41^(st) aspect, said divider has adifferential exhausting structure integrated therein.

According to 43^(rd) aspect of the present invention, in the chargedparticle beam apparatus of 41^(st) or 42^(nd) aspect, said divider has acold trap function.

According to 44^(th) aspect of the present invention, in the chargedparticle beam apparatus of either 41^(st) to 43^(rd) aspect, saiddividers are arranged in two locations including a proximity of thecharged particle beam irradiating location and a proximity of thehydrostatic bearing.

According to 45^(th) aspect of the present invention, in the chargedparticle beam apparatus either of 41^(st) to 44^(th) aspects, the gassupplied to the hydrostatic bearing of said stage is either nitrogen oran inert gas.

According to 46^(th) aspect of the present invention, in the chargedparticle beam apparatus either of 41^(st) to 45^(th) aspects, a surfacetreatment is applied to at least the part of the surface facing thehydrostatic bearing in said XY stage so as to reduce the amount of gasto be desorbed.

According to 47^(th) aspect of the present invention, there is provideda wafer defect inspection apparatus for inspecting a surface of a waferfor defects by using the apparatus disclosed in either of 41^(st) to46^(th) aspects.

According to 48^(th) aspect of the present invention, there is providedan exposing apparatus for delineating a circuit pattern of asemiconductor device on a surface of a semiconductor wafer or a reticleby using the apparatus disclosed in any of 41^(st) to 46^(th) aspects.

According to 49^(th) aspect of the present invention, there is provideda semiconductor manufacturing method for manufacturing a semiconductorby using the apparatus disclosed in any of 41^(st) to 48^(th) aspects.

According to 41^(st) to 49^(th) aspect of the present invention, thefollowing effects may be expected to obtain.

(a) The stage device can enhance accurate positioning within vacuumatmosphere, and further, the pressure in the space surrounding thecharged particle beam irradiating location is hardly increased. That is,it allows the charged particle beam processing to be applied to thesample with high accuracy.

(b) It is almost impossible for gas desorbed or leaked from thehydrostatic bearing to go though the divider and reach the space for thecharged particle beam irradiating system. Thereby, the vacuum level inthe space surrounding the charged particle beam irradiating location canbe further stabilized.

(c) It is harder for the discharged gas to go through to the space forthe charged particle beam irradiating system, and it is easier tomaintain the stability of the vacuum level in the space surrounding thecharged particles beam irradiating location.

(d) The interior of the vacuum chamber is partitioned into threechambers, i.e., a charged particle beam irradiation chamber, ahydrostatic bearing chamber and an intermediate chamber whichcommunicate with each other via a small conductance. Further, the vacuumexhausting system is constructed to control the pressures in therespective chambers sequentially, so that the pressure in the chargedparticle beam irradiation chamber is the lowest, the intermediatechamber medium, and the hydrostatic bearing chamber the highest. Thepressure fluctuation in the intermediate chamber can be reduced by thedivider, and the pressure fluctuation in the charged particle beamirradiation chamber can be further reduced by another step of divider,so that the pressure fluctuation therein can be reduced substantially toa non-problematic level.

(e) The pressure increase upon movement of the stage can be controlledso that it is kept low.

(f) The pressure increase upon movement of the stage can be furthercontrolled to be kept even lower.

(g) Since a defect inspection apparatus with highly accurate stagepositioning performance and with a stable vacuum level in the chargedparticle beam irradiating region can be accomplished, an inspectionapparatus with high inspection performance and without any fear ofcontamination of the sample can be provided.

(h) Since a defect inspection apparatus with highly accurate stagepositioning performance and with a stable vacuum level in the chargedparticle beam irradiating region can be accomplished, an exposingapparatus with high exposing accuracy and without any fear ofcontamination of the sample can be provided.

(i) Manufacturing the semiconductor by using the apparatus with highlyaccurate stage positioning performance and with a stable vacuum level inthe charged particle beam irradiating region can form a miniaturizedmicro semiconductor circuit.

According to 50^(th) aspect of the present invention, there is providedan inspection apparatus or inspection method for inspecting a sample forany defect, which comprises;

an image obtaining means for obtaining respective images for a pluralityof regions to be inspected, said regions being displaced from oneanother while being partially superimposed one on another on saidsample;

a storage means for storing a reference image; and

a defect determination means for determining any defects in said sampleby comparing said respective images obtained by said image obtainingmeans for said plurality of regions to be inspected with said referenceimage stored in said storage means.

According to 51^(st) aspect of the present invention, in the inspectionapparatus or inspection method of 50^(th) aspect, said apparatus furthercomprises a charged particle irradiation means for irradiating a primarycharged particle beam against each of said plurality of regions to beinspected so that a secondary charged particle beam is emitted from saidsample, wherein

said image obtaining means obtains images of said plurality of regionsto be inspected in order by detecting said secondary charged particlebeam emitted from said plurality of regions to be inspected.

According to 52^(nd) aspect of the present invention, in the inspectionapparatus or inspection method of 51^(st) aspect, said charged particleirradiation means comprises a particle source for emitting primarycharged particles and a deflecting means for deflecting said primarycharged particles, wherein

said deflecting means deflects said primary charged particles emittedfrom said particle source so as to be irradiated against said pluralityof regions to be inspected in order.

According to 53^(rd) aspect of the present invention, in the inspectionapparatus or inspection method either of 50^(th) to 52^(nd) aspects,said apparatus comprises a primary optical system for irradiating aprimary charged particle beam against a sample and a secondary opticalsystem for guiding secondary charged particles to a detector.

According to 54^(th) aspect of the present invention, there is provideda semiconductor manufacturing method, which includes a process forinspecting a finished or an under processing of wafer for any defect byusing an inspection apparatus either of 50^(th) to 53^(rd) aspects.

According to 50^(th) to 54the aspect of the present invention, thefollowing advantages are provided.

Since the defect in the sample can be detected by first obtainingrespective images of a plurality of regions to be inspected, which aredisplaced from one another while being partially superimposed one onanother on the sample, and comparing those images of the regions to beinspected with the reference image, any deterioration in the accuracy inthe defect detection can be prevented.

Further, according to the device manufacturing method of the invention,since the defect detection is performed by using such a defectinspection apparatus as described above, the yield of the products canbe improved and the delivery of any faulty products can be prevented.

According to 55^(th) aspect of the present invention, there is providedan apparatus for irradiating a charged particle beam against a sampleloaded on an XY stage, said apparatus characterized in that: said XYstage is accommodated in a housing and supported by a hydrostaticbearing in a non-contact manner with respect to said housing; saidhousing in which said stage is accommodated is exhausted to vacuum; anda differential exhausting mechanism is arranged surrounding a portion insaid charged particle beam apparatus, where the charged particle beam isto be irradiated against a surface of said sample, so that a region onsaid sample to which said charged particle beam is to be irradiated maybe exhausted to vacuum.

According to this invention, a high-pressure gas supplied for thehydrostatic bearing and leaking into the vacuum chamber is primarilyevacuated by a vacuum exhausting pipe connected to the vacuum chamber.Further, arranging the differential exhausting mechanism, whichfunctions to exhaust the region to which the charged particle beam is tobe irradiated, so as to surround the portion on which the chargedparticle beam is to be irradiated, allows the pressure in theirradiation region of the charged particles beam to be decreased to asignificantly lower level than that in the vacuum chamber, thusachieving a stable vacuum level where the processing of the sample bythe charged particle beam can be performed without any problems. That isto say, a stage with a structure similar to that of a stage ofhydrostatic bearing type commonly used in the atmospheric pressure (astage supported by the hydrostatic bearing having no differentialexhausting mechanism) may be used to stably process the sample on thestage by the charged particle beam.

According to 56^(th) aspect of the present invention, in the chargedparticles beam apparatus of 55^(th) aspect, a gas to be supplied to saidhydrostatic bearing of said XY stage is nitrogen or an inert gas, andsaid nitrogen or inert gas is pressurized after having been exhaustedfrom said housing containing said stage so as to be supplied again tosaid hydrostatic bearing.

According to this invention, since the residual gas components in thevacuum housing are inert, there should be no fear that the surface ofthe sample or any surfaces of the structures within the vacuum chamberdefined by the housing would be contaminated by water contents or oiland fat contents, and in addition, even if inert gas molecules areadsorbed onto the sample surface, once being exposed to the differentialexhausting mechanism or the high vacuum section of the irradiationregion of the charged particles beam, said inert gas molecules would bereleased immediately from the sample surface, so that the effect on thevacuum level in the irradiation region of the charged particle beam canbe minimized and the processing applied by the charged particle beam tothe sample can be stabilized.

According to 57^(th) aspect of the present invention, there is provideda wafer defect inspection apparatus for inspecting a surface of asemiconductor wafer for defects by using the apparatus of 55^(th) or56^(th) aspect.

This allows the provision of an inspection apparatus which accomplishespositioning performance of the stage with high precision and alsoprovides a stable vacuum level in the irradiation region of the chargedparticles beam at low cost.

According to 58^(th) aspect of the present invention, there is providedan exposing apparatus for delineating a circuit pattern of asemiconductor device on the surface of a semiconductor wafer or areticle by using the apparatus of 55^(th) or 56^(th) aspect.

This allows the provision of an exposing apparatus which accomplishespositioning performance of the stage with high precision and alsoprovides a stable vacuum level in the irradiation region of the chargedparticles beam at low cost.

According to 59^(th) aspect of the present invention, there is provideda semiconductor manufacturing method for manufacturing a semiconductorby using the apparatus of either of 55^(th) to 58^(th) aspects.

This allows a micro semiconductor circuit to be formed by way ofmanufacturing a semiconductor with the apparatus which accomplishespositioning performance of the stage with high precision and alsoprovides a stable vacuum level in the irradiation region of the chargedparticles beam.

According to the inventions of 55^(th) to 59^(th) aspects, the followingeffects may be expected to obtain.

(A) Processing by the charged particle beam can be stably applied to asample on a stage by the use of the stage having a structure similar tothat of a stage of hydrostatic bearing type which is typically used atatmospheric pressure (a stage supported by the hydrostatic bearinghaving no differential exhausting mechanism).

(B) The effect on the vacuum level in the charged particle beamirradiation region can be minimized, and thereby the processing by thecharged particle beam to the sample can be stabilized.

(C) Such an inspection apparatus can be provided at low cost thataccomplishes positioning performance of the stage with high precisionand provides a stable vacuum level in the irradiation region of thecharged particle beam.

(D) Such an exposing apparatus can be provided in low cost thataccomplishes positioning performance of the stage with high precisionand provides a stable vacuum level in the irradiation region of thecharged particle beam.

(E) A micro semiconductor circuit can be formed by manufacturing thesemiconductor using an apparatus which accomplishes positioningperformance of the stage with high precision and provides a stablevacuum level in the irradiation region of the charged particle beam.

According to 60^(th) aspect of the present invention, there is providedan inspection method for inspecting an object to be inspected byirradiating either of charged particles or electromagnetic waves ontosaid object to be inspected by using an apparatus which comprises:

a working chamber for inspecting said object to be inspected, saidchamber capable of being controlled to be vacuum atmosphere;

a beam source for emitting either of said charged particle or saidelectromagnetic waves as a beam;

an electronic optical system for guiding and irradiating said beam ontosaid object to be inspected held in said working chamber, detecting asecondary charged particles emanated from said object to be inspectedand introducing said secondary charged particles to an image processingsystem;

said image processing system for forming an image by said secondarycharged particle;

an information processing system for displaying and/or storing statusinformation of said object to be inspected based on an output from saidimage processing system; and

a stage unit for operatively holding said object to be inspected so asto be movable with respect to said beam,

wherein said method comprises the steps of:

positioning said beam accurately onto said object to be inspected bymeasuring the position of said object to be inspected;

deflecting said beam onto a desired position of said measured object tobe inspected;

irradiating said desired position on a surface of said object to beinspected by said beam;

detecting a secondary charged particle emanating from said object to beinspected;

forming an image by said secondary charged particles; and

displaying and/or storing status information of said object to beinspected based on output from said image processing system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevation illustrating main components of an inspectionapparatus according to the present invention, viewed along a line A—A inFIG. 2;

FIG. 2A is a plan view of the main components of the inspectionapparatus illustrated in FIG. 1, viewed along a line B—B in FIG. 1;

FIG. 2B is a schematic sectional view of a substrate carrier unitaccording to another embodiment of the invention;

FIG. 3 is a cross-sectional view illustrating a mini-environment chamberin FIG. 1, viewed along a line C—C in FIG. 1;

FIG. 4 is a cross-sectional view illustrating a loader housing in FIG.1, viewed along a line D—D in FIG. 2;

FIGS. 5A and 5B are enlarged views of a wafer rack, wherein FIG. 5A is aside view, and FIG. 5B is a cross-sectional view taken along a line E—Ein FIG. 5A;

FIG. 6 is a diagram illustrating modifications to a method of supportinga main housing;

FIG. 7 is a diagram illustrating modifications to a method of supportinga main housing;

FIG. 8 is a schematic diagram generally illustrating the configurationof an electron-optical system in the inspection apparatus of FIG. 1;

FIG. 9 is a sectional view of the construction of an electron beamdeflecting section of the E×B separator;

FIG. 10 is a sectional view taken along a line A—A in FIG. 9;

FIG. 11 is a schematic general view for explaining an apparatusaccording to one embodiment of the invention;

FIG. 12 is a perspective view of an electrodes, wherein the electrodehas a cylindrical shape formed to be axis-symmetrical,

FIG. 13 is a perspective view of an electrode, wherein the electrode hasa disk-like shape formed to be axis-symmetrical;

FIG. 14 is a graph illustrating a voltage distribution between a waferand an objective lens;

FIG. 15 is a flow chart for the secondary electron detecting operationof an electron beam apparatus;

FIG. 16 is a cross sectional view of an E×B separator according to thepresent invention;

FIG. 17 is a diagram illustrating the electric field distribution of theE×B separator according to the present invention;

FIG. 18 is a schematic diagram of the main components of the prechargeunit of an embodiment according to the present invention;

FIG. 19 is a schematic diagram of a precharge unit of another embodimentaccording to the present invention;

FIG. 20 is a schematic diagram of the precharge unit of still anotherembodiment according to the present invention;

FIG. 21 is a schematic diagram of the precharge unit of yet anotherembodiment according to the present invention;

FIG. 22 is a schematic diagram illustrating an imaging apparatus of oneembodiment according to the present invention;

FIG. 23 is a chart illustrating operational timings for uniforming adistribution or reducing the potential level of electric charge residingon an object in the imaging apparatus of FIG. 22;

FIG. 24 is a schematic diagram of a defect inspection apparatus equippedwith a precharge unit according to another embodiment of the presentinvention;

FIG. 25 is a schematic diagram of a defect inspection apparatus equippedwith a precharge unit according to a further embodiment of the presentinvention;

FIG. 26 is a schematic diagram of a defect inspection apparatus equippedwith a precharge unit according to still further embodiment of thepresent invention;

FIG. 27 is a flow chart showing a flow of a wafer inspection in thedefect inspection apparatus according to any of the embodiments shown inFIGS. 24 to 26;

FIG. 28 is a diagram for explaining specifically a method for inspectinga wafer for any defect in the defect inspection apparatus according toeither of the embodiments shown in FIGS. 24 to 26, wherein (a) shows apattern defect detection, (b) shows a line width measurement, and (c)shows a potential contrast measurement, respectively;

FIG. 29 is a diagram illustrating a potential applying mechanism;

FIGS. 30A and 30B are diagrams for explaining an electron beamcalibration mechanism, wherein FIG. 30A is a side view, and FIG. 30B isa plan view;

FIG. 31 is an explanatory diagram generally illustrating a waferalignment controller;

FIG. 32 is a sectional view of a vacuum chamber and an XY stage of acharged particles beam apparatus of an embodiment according to thepresent invention, wherein (a) is a front elevational view and (b) is aside elevational view;

FIG. 33 is a sectional view of a vacuum chamber and an XY stage of acharged particles beam apparatus of another embodiment according to thepresent invention;

FIG. 34 is a sectional view of a vacuum chamber and an XY stage of acharged particles beam apparatus of an alternative embodiment accordingto the present invention;

FIG. 35 is a sectional view of a vacuum chamber and an XY stage of acharged particles beam apparatus of further alternative embodimentaccording to the present invention;

FIG. 36 is a sectional view of a vacuum chamber and an XY stage of acharged particles beam apparatus of a still further alternativeembodiment according to the present invention;

FIG. 37 is a schematic cross sectional view illustrating a vacuumchamber and an XY stage of a charged particles beam apparatus accordingto an embodiment of the present invention;

FIG. 38 is a schematic diagram illustrating an example of a differentialexhausting mechanism provided in the apparatus shown in FIG. 37;

FIG. 39 is a schematic diagram illustrating a circulating pipe line of agas in the apparatus shown in FIG. 37;

FIG. 40 is a schematic diagram illustrating an example of an opticalsystem and a detecting system to be provided in an optical column;

FIG. 41 is a schematic diagram illustrating an exemplary configurationof a defect inspection apparatus according to a modified embodiment ofthe present invention;

FIG. 42 shows some examples of a plurality of images to be inspectedwhich are obtained by the defect inspection apparatus of FIG. 41, and anexample of a reference image;

FIG. 43 is a flow chart illustrating the flow of the main routine forwafer inspection in the defect inspection apparatus of FIG. 41;

FIG. 44 is a flow chart illustrating the detailed flow of a sub-routinein the process for obtaining image data for a plurality of regions to beinspected (step 1304) of FIG. 43;

FIG. 45 is a flow chart illustrating the detailed flow of a sub-routinein the comparing process (step 1308) of FIG. 43;

FIG. 46 is a schematic diagram illustrating an exemplary configurationof a detector in the defect inspection apparatus of FIG. 41;

FIG. 47 is a schematic diagram illustrating a plurality of regions to beinspected which are displaced one from another while being partiallysuperimposed one on another on the semiconductor wafer surface;

FIG. 48A is a schematic diagram of an electron beam apparatus accordingto another embodiment of the present invention;

FIG. 48B is a schematic plan view illustrating an aspect where aplurality of primary electron beams is scanning a sample in theapparatus of the embodiment shown in FIG. 48A;

FIG. 49A is a view illustrating in more detail a configuration of theapparatus of the embodiment shown in FIG. 48A;

FIG. 49B is a view illustrating an irradiation method of the primaryelectron beam in the apparatus of the same embodiment;

FIG. 50 is a flow chart illustrating an embodiment of a method ofmanufacturing a semiconductor device according to the present invention;

FIG. 51 is a flow chart illustrating a lithography sub-process whichforms the core of a wafer processing process in FIG. 50.

FIG. 52 is a schematic diagram exemplarily illustrating a projectiveelectron beam inspection apparatus;

FIG. 53 is a diagram illustrating the movements of secondary electronsemitted from a rectangular area;

FIG. 54 is a diagram illustrating an electric field distribution of anE×B separator of the prior art.

FIG. 55 is a sectional view of a vacuum chamber and an XY stage in acharged particles beam apparatus according to the prior art, wherein (a)is a front elevational view and (b) is a side elevational view; and

FIG. 56 is a diagram illustrating the relationship between hydrostaticbearings and a differential exhausting mechanism used for the XY stageof FIG. 55.

BEST MODE FOR IMPLEMENTING THE INVENTION

In the following, preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings in connection witha semiconductor inspection apparatus for inspecting, as an object to beinspected, a substrate, i.e., a wafer which has patterns formed on thesurface thereof.

FIGS. 1 and 2A illustrate main components of a semiconductor inspectionapparatus 1 according to an embodiment in elevation and plan view,respectively.

The semiconductor inspection apparatus 1 of this embodiment comprises acassette holder 10 for holding cassettes which store a plurality ofwafers; a mini-environment chamber 20; a main housing 30 which defines aworking chamber; a loader housing 40 disposed between themini-environment chamber 20 and the main housing 30 to define twoloading chambers; a loader 60 for loading a wafer from the cassetteholder 10 onto a stage device 50 disposed in the main housing 30; and anelectron-optical device 70 installed in the vacuum main housing 30.These components are arranged in a positional relationship asillustrated in FIGS. 1 and 2A. The semiconductor inspection apparatus 1further comprises a precharge unit 81 disposed in the vacuum mainhousing 30; a potential applying mechanism 83 (see in FIG. 29) forapplying potential to a wafer; an electron beam calibration mechanism 85(see in FIG. 30); and an optical microscope 871 which forms part of analignment controller 87 for aligning the wafer on the stage device 50.

Cassette Holder

The cassette holder 10 is configured to hold a plurality (two in thisembodiment) of cassettes c (for example, closed cassettes such as SMIF,FOUP manufactured by Assist Co.) in which a plurality (for example, 25)of wafers are stacked in parallel in the vertical direction. Thecassette holder 10 can be arbitrarily selected for installation adaptedto a particular loading mechanism. Specifically, when a cassette,carried to the cassette holder 10, is automatically loaded into thecassette holder 10 by a robot or the like, the cassette holder 10 havinga structure adapted to the automatic loading can be installed. When acassette is manually loaded into the cassette holder 10, the cassetteholder 10 having an open cassette structure can be installed. In thisembodiment, the cassette holder 10 is of a type adapted to the automaticcassette loading, and comprises, for example, an up/down table 11, andan elevating mechanism 12 for moving the up/down table 11 up and down.The cassette c can be automatically set onto the up/down table 11 in astate indicated by chain lines in FIG. 2A. After the setting, thecassette c is automatically rotated to a state indicated by solid linesin FIG. 2A so that it is directed to the axis of pivotal movement of afirst carrier unit within the mini-environment chamber 20. In addition,the up/down table 11 is moved down to a state indicated by chain linesin FIG. 1. In this way, the cassette holder 10 for use in automaticloading, or the cassette holder 10 for use in manual loading may beconfigured in known structures, so that detailed description on theirstructures and functions are omitted.

In another embodiment, as shown in FIG. 2B, a plurality of 300 mmsubstrates is accommodated so that each is contained in a slot-likepocket fixedly mounted in an inner side of a box main body 501 so as tobe transferred and stored. This substrate carrier box 24 is composed ofa box main body 501 of cylinder with angular section, a door 502 forcarrying the substrate in and out, which is coupled with an automaticopening/closing unit of the door for carrying the substrate in and outso as to be capable of mechanically opening and closing an opening in aside face of the box main body 501, a lid body 503 disposed in anopposite side of said opening, for covering another opening throughwhich filters and a fan motor are to be attached or detached, aslot-like pocket (not shown) for holding a substrate W, a ULPA filter505, a chemical filter 506, and a fan motor 507. In this embodiment, thesubstrate is carried in or out by a first carrier unit 612 of robot typein a loader 60.

It should be noted that substrates, i.e., wafers accommodated in thecassette c are wafers subjected to inspecting which is generallyperformed after a process for processing the wafers or in the middle ofthe process within a semiconductor manufacturing processes.Specifically, accommodated in the cassette are substrates or waferswhich have undergone a deposition process, CMP, ion implantation and soon; wafers with circuit patterns on the surface thereof; or wafers whichhave not been formed with circuit patterns. Since a large number ofwafers accommodated in the cassette c are spaced from each other in thevertical direction and arranged in parallel, the first carrier unit hasan arm which is vertically movable such that a wafer at an arbitraryposition can be held by the first carrier unit, as described later indetail.

Mini-Environment Chamber

In FIGS. 1 through 3, the mini-environment chamber 20 comprises ahousing 22 which defines a mini-environment space 21 with a controlledatmosphere; a gas circulator 23 for circulating a gas such as clean airwithin the mini-environment space 21 for the atmosphere control; adischarger 24 for recovering a portion of air supplied into themini-environment space 21 for discharging; and a pre-aligner 25 forroughly aligning a substrate, i.e., a wafer to be inspected, which isplaced in the mini-environment space 21.

The housing 22 has a top wall 221, a bottom wall 222, and peripheralwall(s) 223 which surrounds four sides of the housing 22 to provide astructure for isolating the mini-environment space 21 from the outside.For controlling the atmosphere in the mini-environment space 21, the gascirculator 23 comprises a gas supply unit 231 attached to the top wall221 within the mini-environment space 21 as illustrated in FIG. 3 forcleaning a gas (air in this embodiment) and delivering the cleaned gasdownward through one or more gas nozzles (not shown) in laminar flow; arecovery duct 232 disposed on the bottom wall 222 within themini-environment space for recovering air which has flowed to thebottom; and a conduit 233 for connecting the recovery duct 232 to thegas supply unit 231 for returning recovered air to the gas supply unit231. In this embodiment, the gas supply unit 231 constantly replacesabout 20% of air to be supplied, with the air taken from the outside ofthe housing 22 for cleaning. However, the percentage of gas taken fromthe outside may be arbitrarily selected. The gas supply unit 231comprises an HEPA or ULPA filter of a known structure for creatingcleaned air. The laminar downflow of cleaned air is mainly supplied suchthat the air passes a carrying surface of the first carrier unit 61,later described, disposed within the mini-environment space 21 toprevent dust particles, which could be produced by the carrier unit,from attaching to the wafer. Therefore, the downflow nozzles need not bepositioned near the top wall as illustrated, but are only required to beabove the carrying surface of the carrier unit 61. In addition, the airneed not be supplied over the entire mini-environment space 21. Itshould be noted that an ion wind may be used as cleaned air to ensurethe cleanliness as the case may be. Also, a sensor may be providedwithin the mini-environment space 21 for observing the cleanliness suchthat the apparatus is shut down when the cleanliness is below apredetermined level. An access port 225 is formed in a portion of theperipheral wall 223 of the housing 22 that is adjacent to the cassetteholder 10. A shutter device of a known structure may be provided nearthe access port 225 to shut the access port 225 from themini-environment chamber 20. The laminar downflow near the wafer may be,for example, at a rate of 0.3 to 0.4 m/sec. The gas supply unit 231 maybe disposed outside the mini-environment space 21 instead of within themini-environment space 21.

The discharger 24 comprises a suction duct 241 disposed at a positionbelow the wafer carrying surface of the carrier unit 61 and below thecarrier unit 61; a blower 242 disposed outside the housing 22; and aconduit 243 for connecting the suction duct 241 to the blower 242. Thedischarger 24 sucks a gas flowing down around the carrier unit andincluding dust, which could be produced by the carrier unit, through thesuction duct 241, and discharges the gas outside the housing 22 throughthe conduits 243, 244 and the blower 242. In this event, the gas may bedischarged into an exhaust pipe (not shown) which is laid to thevicinity of the housing 22.

The aligner 25 disposed within the mini-environment space 21 opticallyor mechanically detects an orientation flat (which refers to a flatportion formed along the outer periphery of a circular wafer) formed onthe wafer, or one or more V-shaped notches formed on the outerperipheral edge of the wafer to previously align the orientation of thewafer in a rotating direction about the axis of the wafer at an accuracyof approximately ± one degree. The pre-aligner forms part of a mechanismfor determining the coordinates of an object to be inspected, which is afeature of the claimed invention, and is responsible for rough alignmentof an object to be inspected. Since the pre-aligner itself may be of aknown structure, description on its structure and operation is omitted.

Though not shown, a recovery duct for the discharger 24 may also beprovided below the pre-aligner such that air including dust, dischargedfrom the pre-aligner, is discharged to the outside.

Main Housing

In FIGS. 1 and 2, the main housing 30, which defines the working chamber31, comprises a housing body 32 that is supported by a housingsupporting device 33 carried on a vibration isolator 37 disposed on abase frame 36. The housing supporting device 33 comprises a framestructure 331 assembled into a rectangular form. The housing body 32comprises a bottom wall 321 securely carried on the frame structure 331;a top wall 322; and a peripheral wall 323 which is connected to thebottom wall 321 and the top wall 322 and surrounds four sides of thehousing body 32, and isolates the working chamber 31 from the outside.In this embodiment, the bottom wall 321 is made of a relatively thicksteel plate to prevent distortion due to the weight of equipment carriedthereon such as the stage device 50. Alternatively, another structuremay be employed. In this embodiment, the housing body 32 and the housingsupporting device 33 are assembled into a rigid construction, and thevibration isolator 37 blocks vibrations from the floor, on which thebase frame 36 is installed, from being transmitted to the rigidstructure. A portion of the peripheral wall 323 of the housing body 32that adjoins the loader housing 40, later described, is formed with anaccess port 325 for introducing and removing a wafer.

The vibration isolator 37 may be either of an active type which has anair spring, a magnetic bearing and so on, or a passive type likewisehaving these components. Since any known structure may be employed forthe vibration isolator 37, description on the structure and functions ofthe vibration isolator itself is omitted. The working chamber 31 is heldin a vacuum atmosphere by a vacuum system (not shown) of a knownstructure. A controller 2 for controlling the operation of the overallapparatus is disposed below the base frame 36.

Loader Housing

In FIGS. 1, 2 and 4, the loader housing 40 comprises a housing body 43which defines a first loading chamber 41 and a second loading chamber42. The housing body 43 comprises a bottom wall 431; a top wall 432; aperipheral wall 433 which surrounds four sides of the housing body 43;and a partition wall 434 for partitioning the first loading chamber 41and the second loading chamber 42 such that both the loading chamberscan be isolated from the outside. The partition wall 434 is formed withan opening, i.e., an access port 435 for passing a wafer between boththe loading chambers. Also, a portion of the peripheral wall 433 thatadjoins the mini-environment device 20 and the main housing 30 is formedwith access ports 436, 437. The housing body 43 of the loader housing 40is carried on and supported by the frame structure 331 of the housingsupporting device 33. This prevents vibrations from the floor from beingtransmitted to the loader housing 40 as well. The access port 436 of theloader housing 40 is in alignment with the access port 226 of thehousing 22 of the mini-environment device 20, and a shutter device 27 isprovided for selectively blocking communication between themini-environment space 21 and the first loading chamber 41. The shutterdevice 27 has a sealing material 271 which surrounds the peripheries ofthe access ports 226, 436 and is fixed to the side wall 433 in closecontact therewith; a door 272 for blocking air from flowing through theaccess ports in cooperation with the sealing material 271; and a driver273 for moving the door 272. Likewise, the access port 437 of the loaderhousing 40 is in alignment with the access port 325 of the housing body32, and a shutter 45 is provided for selectively blocking communicationbetween the second loading chamber 42 and the working chamber 31 in ahermetic manner. The shutter 45 comprises a sealing material 451 whichsurrounds the peripheries of the access ports 437, 325 and is fixed toside walls 433, 323 in close contact therewith; a door 452 for blockingair from flowing through the access ports in cooperation with thesealing material 451; and a driver 453 for moving the door 452. Further,the opening 435 formed through the partition wall 434 is provided with ashutter 46 for closing the opening with the door 461 to selectivelyblocking communication between the first and second loading chambers ina hermetic manner. These shutter devices 27, 45, 46 are configured toprovide air-tight sealing for the respective chambers when they are in aclosed state. Since these shutter devices may be implemented by knownones, detailed description of their structures and operations isomitted. It should be noted that the method of supporting the housing 22of the mini-environment device 20 is different from the method ofsupporting the loader housing 40. Therefore, for preventing vibrationsfrom being transmitted from the floor through the mini-environmentdevice 20 to the loader housing 40 and the main housing 30, avibration-proof cushion material may be disposed between the housing 22and the loader housing 40 to provide air-tight sealing for theperipheries of the access ports.

Within the first loading chamber 41, a wafer rack 47 is disposed forsupporting a plurality (two in this embodiment) of wafers spaced in thevertical direction and maintained in a horizontal state. As illustratedin FIG. 5, the wafer rack 47 comprises posts 472 fixed at four cornersof a rectangular base plate 471, spaced from one another, in an uprightstate. Each of the posts 472 is formed with supporting portions 473, 474in two stages, such that peripheral edges of wafers W are carried on andheld by these supporting portions. Then, leading ends of arms of thefirst and second carrier units 61, 63, later described, are broughtcloser to wafers from adjacent posts and grasp the wafers.

The atmosphere of the loading chambers 41, 42 can be controlled so as tobe maintained in a high vacuum state (at a vacuum degree of 10⁻⁵ to 10⁻⁶Pa) by a vacuum evacuator (not shown) in a known structure including avacuum pump, not shown. In this event, the first loading chamber 41 maybe held in a low vacuum atmosphere as a low vacuum chamber, while thesecond loading chamber 42 may be held in a high vacuum atmosphere as ahigh vacuum chamber, to effectively prevent contamination of wafers. Theemployment of such a structure allows a wafer, which is accommodated inthe loading chamber and is next subjected to the defect inspection, tobe carried into the working chamber without delay. The employment ofsuch a loading chambers provides for an improved throughput for thedefect inspection, and the highest possible vacuum state around theelectron beam source which is required to be kept in a high vacuumstate, together with the principle of a multi-beam type electron device,later described.

The first and second loading chambers 41, 42 are connected to a vacuumexhaust pipe and a vent pipe for an inert gas (for example, dried purenitrogen) (neither of which are shown), respectively. In this way, theatmospheric state within each loading chamber is attained by an inertgas vent (which injects an inert gas to prevent oxygen and non-inertgases from contacting the surface). Since an apparatus itself forimplementing the inert gas vent is known in structure, detaileddescription thereon is omitted.

In the inspection apparatus according to the present invention whichuses an electron beam, when representative lanthanum hexaborate (LaB₆)used as an electron beam source for an electron-optical system, laterdescribed, is heated once to such a high temperature that it causesemission of thermal electrons, it should be exposed to oxygen as littleas possible so as not to shorten its lifetime. The exposure of theelectron beam source to oxygen can be prevented by carrying out theatmosphere control as mentioned above before introducing a wafer intothe working chamber in which the electron-optical system is disposed.

Stage Device

The stage device 50 comprises a fixed table 51 disposed on the bottomwall 321 of the main housing 30; a Y-table 52 movable in the Y-directionon the fixed table 51 (the direction vertical to the drawing sheet inFIG. 1); an X-table 53 movable in the X-direction on the Y-table 52 (inthe left-to-right direction in FIG. 1); a turntable 54 rotatable on theX-table; and a holder 55 disposed on the turntable 54. A wafer W isreleasably held on a wafer carrying surface 551 of the holder 55. Theholder 55 may be of a known structure which is capable of releasablyholding a wafer by means of a mechanical or electrostatic chuck feature.The stage device 50 uses servo motors, encoders and a variety of sensors(not shown) to operate a plurality of tables as mentioned above topermit highly accurate alignment of a wafer W held on the carryingsurface 551 by the holder 55 in the X-direction, Y-direction andZ-direction (in the up-down direction in FIG. 1) with respect to anelectron beam irradiated from the electron-optical system 70, and in adirection about the axis normal to the wafer supporting surface (θdirection). The alignment in the Z-direction may be made such that theposition on the carrying surface 551 of the holder 55, for example, canbe finely adjusted in the Z-direction. In this event, a referenceposition on the carrying surface 551 is sensed by a position measuringdevice using a laser of small diameter (a laser interference rangefinder using the principles of interferometer) to control the positionby a feedback circuit, not shown. Additionally or alternatively, theposition of a notch or the orientation flat of a wafer is measured tosense the plane position and the rotational position of the waferrelative to the electron beam to control the position of the wafer byrotating the turntable 54 by a stepping motor which can be controlled inextremely small angular increments. In order to maximally prevent dustproduced within the working chamber, servo motors 531, 531 and encoders522, 532 for the stage device 50 are disposed outside the main housing30. Since the stage device 50 may be of a known structure used, forexample, in steppers and so on, detailed description of its structureand operation is omitted. Likewise, since the laser interference rangefinder may also be of a known structure, detailed description of itsstructure and operation is also omitted.

It is also possible to establish a basis for signals which are generatedby previously inputting a rotational position, and X-, Y-positions of awafer relative to the electron beam in a signal detecting system or animage processing system, later described. The wafer chucking mechanismprovided in the holder 55 is configured to apply a voltage for chuckinga wafer to an electrode of an electrostatic chuck, and the alignment ismade by holding three points on the outer periphery of the wafer(preferably spaced equally in the circumferential direction). The waferchucking mechanism comprises two fixed aligning pins and a push-typeclamp pin. The clamp pin can effect automatic chucking and automaticreleasing, and constitutes an electric conducting portion for applyingthe voltage.

While in this embodiment, the X-table is defined as a table which ismovable in the left-to-right or right-to-left direction in FIG. 2; andthe Y-table as a table which is movable in the up-down direction, atable movable in the left-to-right or right-to-left direction in FIG. 2may be defined as the Y-table; and a table movable in the up-downdirection as the X-table.

Loader

The loader 60 comprises a robot-type first carrier unit 61 disposedwithin the housing 22 of the mini-environment device 20; and arobot-type second carrier unit 63 disposed within the second loadingchamber 42.

The first carrier unit 61 comprises an articulated arm 612 rotatableabout an axis O₁—O₁ with respect to a driver 611. While an arbitrarystructure may be used for the articulated arm, the articulated arm inthis embodiment has three parts which are pivotably attached to eachother. One part of the arm 612 of the first carrier unit 61, i.e., thefirst part closest to the driver 611 is attached to a rotatable shaft613 by a driving mechanism (not shown) of a known structure, disposedwithin the driver 611. The arm 612 is pivotable about the axis O₁—O₁ bymeans of the shaft 613, and radially telescopic as a whole with respectto the axis O₁—O₁ through relative rotations among the parts. At aleading end of the third part of the arm 612 furthest away from theshaft 613, a clamp 616 in a known structure for clamping a wafer, suchas a mechanical chuck or an electrostatic chuck, is disposed. The driver611 is movable in the vertical direction by an elevating mechanism 615is of a known structure.

The first carrier unit 61 extends the arm 612 in either a direction M1or a direction M2 within two cassettes c held in the cassette holder 10,and removes a wafer accommodated in a cassette c by carrying the waferon the arm or by clamping the wafer with the chuck (not shown) attachedat the leading end of the arm. Subsequently, the arm is retracted (in astate as illustrated in FIG. 2), and then rotated to a position at whichthe arm can extend in a direction M3 toward the pre-aligner 25, andstopped at this position. Then, the arm is extended to transfer thewafer held on the arm to the pre-aligner 25. After receiving a waferfrom the pre-aligner 25, contrary to the foregoing, the arm is furtherrotated and stopped at a position at which it can extend to the secondloading chamber 41 (in the direction M4), and transfers the wafer to awafer receiver 47 within the second loading chamber 41. For mechanicallyclamping a wafer, the wafer should be clamped at a peripheral region (ina range of approximately 5 mm from the peripheral edge). This is becausethe wafer is formed with devices (circuit pattern) over the entiresurface except for the peripheral region, and clamping the inner regionwould result in failed or defective devices.

The second carrier unit 63 is basically identical to the first carrierunit 61 in structure except that the second carrier unit 63 carries awafer between the wafer rack 47 and the carrying surface of the stagedevice 50, so that detailed description thereon is omitted.

In the loader 60, the first and second carrier units 61, 63 carry awafer from a cassette held in the cassette holder 10 to the stage device50 disposed in the working chamber 31 and vice versa, while keeping thewafer substantially in a horizontal state. The arms of the carrier unitsare moved in the vertical direction only when a wafer is removed fromand inserted into a cassette, when a wafer is carried on and removedfrom the wafer rack, and when a wafer is carried on and removed from thestage device 50. It is therefore possible to smoothly carry a wafer evenif it is a large one, for example, a wafer having a diameter of 30 cm.

Transfer of Wafer

Next, how a wafer is transferred in the apparatus will be described insequence from the cassette c held by the cassette holder 10 to the stagedevice 50 disposed in the working chamber 31.

As described above, when the cassette is manually set, the cassetteholder 10 having a structure adapted to the manual setting is used, andwhen the cassette is automatically set, the cassette holder 10 having astructure adapted to the automatic setting is used. In this embodiment,as the cassette c is set on the up/down table 11 of the cassette holder10, the up/down table 11 is moved down by the elevating mechanism 12 toalign the cassette c with the access port 225.

As the cassette is aligned with the access port 225, a cover (not shown)provided for the cassette is opened, and a cylindrical cover is appliedbetween the cassette c and the access port 225 of the mini-environmentto block the cassette and the mini-environment space 21 from theoutside. Since these structures are known, detailed description of theirstructures and operations is omitted. When the mini-environment device20 is provided with a shutter for opening and closing the access port225, the shutter is operated to open the access port 225.

On the other hand, the arm 612 of the first carrier unit 61 remainsoriented in either the direction M1 or M2 (in the direction M2 in thisdescription). As the access port 225 is opened, the arm 612 extends toreceive one of wafers accommodated in the cassette at the leading end.While the arm and a wafer to be removed from the cassette are adjustedin the vertical position by moving up or down the driver 611 and the arm612 of the first carrier unit 61 in this embodiment, the adjustment maybe made by moving the up/down table 11 of the cassette holder 10, ormade by both.

As the arm 612 receives the wafer, the arm 621 is retracted, and theshutter is operated to close the access port (when the shutter isprovided). Next, the arm 612 is pivoted about the axis O₁—O₁ such thatit can extend in the direction M3. Then, the arm 612 is extended andtransfers the wafer carried at the leading end or clamped by the chuckonto the pre-aligner 25 which aligns the orientation of the rotatingdirection of the wafer (the direction about the central axis vertical tothe wafer plane) within a predetermined range. Upon completion of thealignment, the carrier unit 61 retracts the arm 612 after a wafer hasbeen received from the prealigner 25 to the leading end of the arm 612,and rotates the arm 612 to a position in which the arm 612 can beextended in a direction M4. Then, the door 272 of the shutter device 27is moved to open the access ports 226, 436, and the arm 612 is extendedto place the wafer on the upper stage or the lower stage of the waferrack 47 within the first loading chamber 41. It should be noted thatbefore the shutter device 27 opens the access ports 226, 436 to transferthe wafer to the wafer rack 47, the opening 435 formed through thepartition wall 434 is closed by the door 461 of the shutter 46 in anair-tight state.

In the process of carrying a wafer by the first carrier unit, clean airflows (as downflow) in laminar flow from the gas supply unit 231disposed on the housing of the mini-environment device to prevent dustfrom attaching to the upper surface of the wafer while being carried. Aportion of the air near the carrier unit (in this embodiment, about 20%of the air supplied from the supply unit 231, which is substantiallycontaminated air) is sucked from the suction duct 241 of the discharger24 and discharged outside the housing. The remaining air is recoveredthrough the recovery duct 232 disposed on the bottom of the housing andreturned again to the gas supply unit 231.

As the wafer is placed into the wafer rack 47 within the first loadingchamber 41 of the loader housing 40 by the first carrier unit 61, theshutter device 27 is closed to seal the loading chamber 41. Then, thefirst loading chamber 41 is filled with an inert gas to expel air.Subsequently, the inert gas is also discharged so that a vacuumatmosphere dominates within the loading chamber 41. The vacuumatmosphere within the loading chamber 41 may be at a low vacuum degree.When a certain degree of vacuum is formed within the loading chamber 41,the shutter 46 is operated to open the access port 434 which has beensealed by the door 461, and the arm 632 of the second carrier unit 63 isextended to receive one wafer from the wafer receiver 47 with the clampat the leading end (the wafer is carried on the leading end or clampedby the chuck attached to the leading end). Upon completion of thereceipt of the wafer, the arm 632 is retracted, followed by the shutter46 again operated to close the access port 435 by the door 461. Itshould be noted that the arm 632 previously takes a posture in which itcan extend in the direction N1 of the wafer rack 47 before the shutter46 is operated to open the access port 435. Also, as described above,the access ports 437, 325 are closed by the door 452 of the shutter 45before the shutter 46 is opened to block communication between thesecond loading chamber 42 and the working chamber 31 in an air-tightstate, so that the second loading chamber 42 can be evacuated.

As the shutter 46 is operated to close the access port 435, the secondloading chamber 42 is again evacuated at a higher degree of vacuum thanthe first loading chamber 41. Meanwhile, the arm 632 of the secondcarrier unit 63 is rotated to a position from which it can extend towardthe stage device 50 within the working chamber 31. On the other hand, inthe stage device 50 within the working chamber 31, the Y-table 52 ismoved upward, as viewed in FIG. 2, to a position at which the centerline X₀—X₀ of the X-table 53 substantially aligns with an X-axis X₁—X₁which passes a pivotal axis O₂—O₂ of the second carrier unit 63. TheX-table 53 in turn is moved to the position closest to the leftmostposition in FIG. 2, and remains at this position. When the secondloading chamber 42 is evacuated to substantially the same degree ofvacuum as the working chamber 31, the door 452 of the shutter 45 ismoved to open the access ports 437, 325, allowing the arm 632 to extendso that the leading end of the arm 632, which holds a wafer, approachesthe stage device 50 within the working chamber 31. Then, the wafer isplaced on the carrying surface 551 of the stage device 50. As the waferhas been placed on the carrying surface 551, the arm 632 is retracted,followed by the shutter 45 operated to close the access ports 437, 325.

The foregoing description has been made about the operations in which awafer in the cassette c is carried and placed on the stage device 50.For returning a wafer, which has been carried on the stage device 50 andprocessed, from the stage device 50 to the cassette c, the operationreverse to the foregoing is performed. Since a plurality of wafers arestored in the wafer rack 47, the first carrier unit 61 can carry a waferbetween the cassette and the wafer rack 47 while the second carrier unit63 can carry a wafer between the wafer rack 47 and the stage device 50,so that the inspecting operation can be efficiently carried out.

Specifically, when there is a wafer A, which has been already beenprocessed, and a wafer B, which has not yet been processed, in a waferrack 47 of a second carrier unit,

(1) at first, the wafer B which has not yet been processed istransferred to the stage 50 and the processing is started;

(2) during this processing, the wafer A which has already been processedis transferred from the stage 50 to the wafer rack 47 by an arm, a waferC which has not yet been processed is picked up from the wafer rackagain by the arm, which after having been positioned by a pre-aligner,is further transferred to the wafer rack 47 of a loading chamber 41.

This procedure may allow the wafer A, which has already been processed,to be substituted by the wafer C, which has not yet been processed, inthe wafer rack 47, during processing of wafer B.

Alternatively, depending on how such an apparatus executes an inspectionand/or an evaluation, a plurality of stage units 50 may be arranged inparallel, and in this case, wafers are transferred from one wafer rack47 for each of the stage units 50, thereby providing simultaneousprocessing of a plurality of wafers.

FIG. 6 illustrates typical modifications to the method of supporting themain housing 30. In an typical modification illustrated in FIG. 6, ahousing supporting device 33 a is made of a thick rectangular steelplate 331 a, and a housing body 32 a is carried on the steel plate.Therefore, the bottom wall 321 a of the housing body 32 a is thinnerthan the bottom wall 222 of the housing body 32 in the foregoingembodiment. In a typical modification illustrated in FIG. 7, a housingbody 32 b and a loader housing 40 b are suspended from a frame structure336 b of a housing supporting device 33 b. Lower ends of a plurality ofvertical frames 337 b fixed to the frame structure 336 b are fixed tofour corners of a bottom wall 321 b of the housing body 32 b, such thatthe peripheral wall and the top wall are supported by the bottom wall.Then, a vibration isolator 37 b is disposed between the frame structure336 b and a base frame 36 b. Likewise, the loader housing 40 b issuspended by a suspending member 49 b fixed to the frame structure 336.In the typical modification of the housing body 32 b illustrated in FIG.7, the housing body 32 b is supported in suspension, the center ofgravity of the main housing and a variety of devices disposed therein,as a whole, can be brought downward. The methods of supporting the mainhousing and the loader housing, including the typical modificationsdescribed above, are configured to prevent vibrations from beingtransmitted from the floor to the main housing and the loader housing.

In another typical modification, not shown, only the housing body of themain housing is supported by the housing supporting device from below,while the loader housing may be placed on the floor in the same way asthe adjacent mini-environment device. Alternatively, in a furthertypical modification, not shown, only the housing body of the mainhousing is supported by suspension from the frame structure, while theloader housing may be placed on the floor in the same way as theadjacent mini-environment device.

According to the subject embodiment, the following advantages areprovided:

(A) the general configuration can be established for an inspectionapparatus in accordance with an electron beam based projection scheme,which can process objects under inspection at a high throughput;

(B) a clean gas is forced to flow onto an object to be inspected withinthe mini-environment space to prevent dust from attaching to the objectto be inspected, and a sensor is provided for observing the cleanliness,thereby making it possible to inspect the object to be inspected whilemonitoring dust within the space;

(C) when the loading chamber and the working chamber are integrallysupported through a vibration isolator, an object to be inspected can becarried to the stage device and inspected thereon without being affectedby the external environment.

Electron-Optical-System

The electron-optical system 70 comprises a column 71 fixed on thehousing body 32. Disposed within the column 71 are an electron-opticalsystem comprised of a primary electron-optical system (hereinaftersimply called the “primary optical system”) 72 and a secondaryelectron-optical system (hereinafter simply called the “secondaryoptical system”) 74, and a detecting system 76, as illustrated generallyin FIG. 8. The primary optical system 72, which is an optical system forirradiating the surface of a wafer W to be inspected with an electronbeam, comprises an electron gun 721 for emitting an electron beam; alens system 722 comprised of electrostatic lenses for converging aprimary electron beam emitted from the electron gun 721; a Wien filter,i.e., an E×B separator 723; and an objective lens system 724. Thesecomponents are arranged in order with the electron gun 721 placed at thetop, as illustrated in FIG. 8. The lenses constituting the objectivelens system 724 in this embodiment are retarding field type objectivelenses. In this embodiment, the optical axis of the primary electronbeam emitted from the electron gun 721 is oblique to the optical axis ofirradiation along which the wafer W to be inspected is irradiated withthe electron beam (perpendicular to the surface of the wafer).Electrodes 725 are disposed between the objective lens system 724 andthe wafer W to be inspected. The electrodes 725 are axially symmetricabout the optical axis of irradiation of the primary electron beam, andcontrolled in voltage by a power supply 726.

The secondary optical system 74 comprises a lens system 741 comprised ofelectrostatic lenses which pass secondary electrons separated from theprimary optical system by an E×B deflector 723. This lens system 741functions as a magnifier for enlarging a secondary electron image.

The detecting system 76 comprises a detector 761 and an image processingunit 763 which are disposed on a focal plane of the lens system 741.

Electron Gun (Electron Beam Source)

A thermal electron beam source is employed as an electron beam source.Cathode is L_(a)B₆. Other material may be used for the cathode so far asit has a high melting point (low vapor pressure at high temperature) anda small work function. The cathode with its tip portion formed into coneshape or the emitter member formed into trapezoidal cone shape with thetip portion of the cone having been cut away may be used. The diameterof the tip of the trapezoidal cone may be about 100 μm. Although inother methods, an electron beam source of the field emission type or thethermal field emission type has been used, in such a case where arelatively large area (for example, 100×25 to 400×100 μm²) is irradiatedwith a high current (in the order of 1 μA) as is the case of the presentinvention, most preferably the thermal electron source using L_(a)B₆should be employed. (In the SEM method, typically the thermal fieldelectron beam source is used.) It is to be appreciated that the thermalelectron beam source is one method in which the cathode is heated toemit an electron, while the thermal electric field emission electronbeam source is one method in which a high electric field is applied tothe cathode to emit an electron and further the electron emittingsection is heated so as to stabilize the emission of electrons.

Primary Optical System

A section for forming an electron beam irradiated from an electron gunand irradiating the electron beam against a wafer surface, which forms arectangle or circle (ellipse) on said wafer surface, said section iscalled the primary optical system. Controlling the lens condition in theprimary optical system allows control of a beam size and/or a currentdensity. Further, an E×B filter (Wien filter) disposed in couplingsections of the primary and the secondary electronic optical systemscontrols the primary electron beam so that it enters the wafer at rightangles.

The thermal electrons emitted from a L_(a)B₆ cathode are formed into across-over image on a gun aperture by using a Wehnelt triple-anode lens.The electron beam, whose angle of incidence to the lens has beenappropriately adjusted by a lighting field stop, is formed into an imageon a NA aperture in a rotationally asymmetrical form by controlling theelectrostatic lens in the primary electronic optical system, and thenirradiated onto the wafer surface as a plane. The rear stage of theelectrostatic lens in the primary electronic optical system is composedof a triple stage quadrupole (QL) and a single stage of electrode forcorrecting the aperture aberration. The quadrupole lens requires strictalignment accuracy but has a stronger focusing effect than arotationally symmetrical lens, and thereby the aperture aberrationcorresponding to the spherical aberration of the rotationallysymmetrical lens can be corrected by applying an appropriate voltage tothe aperture aberration correcting electrode. Thereby, a uniform planebeam can be irradiated over a specified region.

Secondary Electronic Optical System

A two-dimensional secondary electron image generated by an electron beamirradiated onto a wafer is formed into an image by electrostatic lenses(CL, TL) corresponding to an objective lens on a location of field stopand magnified and projected by a subsequent stage of lens (PL). Saidimage-forming and projecting optical system is called the secondaryoptical system.

At that time, a negative bias voltage (decelerating electric fieldvoltage) is applied to the wafer. The decelerating electric fieldeffectively decelerates the irradiation beam to reduce damage in thesample, while it accelerates secondary electrons emitted from the samplesurface using the potential difference between the CL and the wafer toreduce chromatic aberration. Electrons focused by the CL are furtherformed into an image on a FA by the TL, which image is then magnifiedand projected by the PL so as to be formed into an image on a secondaryelectron detector (MCP). In the present optical system, a NA ispositioned between the CL and the TL, so that the optical system can beconstructed in which an extra-axis aberration may be reduced byoptimizing the NA.

Further, in order to correct errors in the fabrication of the electronicoptical systems and/or astigmatism or an anisotropic magnification of animage resulting from electrons passing through an E×B filter (a Wienfilter), an electrostatic octopole (STIG) is disposed to make acorrection, while in order to deal with the problem of an axial offset,deflectors (OP) are arranged between respective lenses so as to make thecorrection. This yields a projecting optical system with a uniformedresolution in the field of view.

E×B Unit (Wien Filter)

An E×B unit is a unit of electromagnetic prism optical system, in whichan electrode and a magnetic pole are arranged in the directionsorthogonal to each other so that an electric field and a magnetic fieldcross at right angles. If the electromagnetic field is selectively givenappropriately, a condition (the Wien condition) can be made where anelectron beam entering into the field from one direction is deflected,while in the electron beam entering from the opposite direction, a forceapplied by the electric field and another force applied by the magneticfield are offset to each other, and thereby the primary electron beam isdeflected to be irradiated onto the wafer at right angles and thesecondary electron beam advances straight ahead toward the detector.

The detailed configuration of an electron beam deflecting section 723will be described with reference to FIGS. 9 and 10 illustrating alongitudinal sectional view taken along the line A—A of FIG. 9. As shownin FIG. 9, a field in the electron beam deflecting section is structuredsuch that the electric field is crossed with the magnetic field at rightangles in a plane normal to the optical axis of said projecting opticalsystem, that is, an E×B structure.

In this regard, the electric field may be generated by electrodes 723-1and 723-2, each having a curved surface of concave shape. The electricfields generated by the electrodes 723-1 and 723-2 are respectivelycontrolled by control sections 723 a and 723 b. On the other hand,arranging the electromagnetic coils 723-1 a and 723-2 a so as to becrossed with the electrodes 723-1 and 723-2 for generating the electricfield allows the magnetic field to be generated. It is to be noted thatthose electrodes 723-1 and 723-2 for generating the electric field arearranged to be point-symmetrical (but may also be arranged in concentriccircles).

In this case, in order to improve the uniformity of the magnetic field,a magnetic path 42 is formed with a pole piece in the form of parallelplate shape. The behavior of the electron beam on the longitudinal crosssectional plane taken along the A—A line is shown in FIG. 10. Theirradiated electron beams 711 a and 711 b, after having been deflectedby the electric field generated by the electrodes 723-1 and 723-2 andthe magnetic field generated by the electromagnetic coils 723-1 a and723-2 a, enter onto the sample surface in the vertical direction.

In this configuration, the positions and the angles of incidence of theirradiation electron beams 711 a and 711 b to the electron beamdeflecting section 723 are univocally determined as the energy of theelectron is determined. In addition, in order to advance the secondaryelectrons 712 a and 712 b straight ahead, the respective controlsections 723 a and 723 d, and 723 c and 723 b control the electric fieldgenerated by the electrodes 723-1 and 723-2 and the magnetic fieldgenerated by the electromagnetic coils 723-1 a and 723-2 a so that thecondition for the electric field and the magnetic field may be shown asvB=E, and thereby the secondary electrons are allowed to go straightthrough the electron beam deflecting section 723 into said projectingoptical section. Where, V is a velocity of the electrons (m/s), B is themagnetic field (T), e is an amount of the electric charge (C) and E isthe electric field (V/m).

Detector

A secondary electron image from the wafer, which is formed into an imageby the secondary optical system, is primarily amplified in themicro-channel plate (MCP) and then impinges against a fluorescent screento be converted into an optical image. As for the principle of the MCP,millions of very thin glass capillaries made of conductive material,each having a diameter of 6 to 25 μm and a length of 0.24 to 1.0 mm, arebundled and formed into a thin plate, and application of a specifiedvoltage makes each of the capillaries work as an individual secondaryelectron amplifier so as to form the secondary electron amplifier as awhole.

The image that has been converted into the light by said detector isprojected on the TDI-CCD by the FOP system disposed in the atmospherethrough a vacuum permeable window on a one-to-one basis.

Next, the operation of the electron-optical device 70 configured asdescribed above will be described.

As shown in FIG. 8, the primary electron beam emitted from the electrongun 721 is converged by the lens system 722. The converged primaryelectron beam enters the E×B deflector 723, is deflected so that it isirradiated vertical to the surface of the wafer W, and focused on thesurface of the wafer W by the objective lens system 724.

The secondary electrons emitted from the wafer by the irradiation of theprimary electron beam are accelerated by the objective lens system 724,enter the E×B deflector 723, travels straight through the deflector 723,and are lead to the detector 761 by the lens system 741 of the secondaryoptical system. Then, the secondary electrons are detected by thedetector 761 which generates a detection signal for an image processingunit 763.

Assume in this embodiment that the objective lens system 724 is appliedwith a high voltage in a range of 10 to 20 kV, and that a wafer has beenprepared in place.

Here, when the electrodes 725 are applied with a voltage of −200 V ifthe wafer W includes a via b, an electric field of 0 to −0.1 V/mm (“−”indicates that the wafer W has a higher potential) is produced on thesurface of the wafer W irradiated with the electron beam. In this state,although the wafer W can be inspected for defects without causing adischarge between the objective lens system 724 and the wafer W, aslight degradation is experienced in the efficiency of detecting thesecondary electrons. Therefore, a sequence of operations involvingirradiating the electron beam and detecting the secondary electrons isperformed, for example, four times, such that the results of the fourdetections are applied with processing such as accumulative addition,averaging operation and so on to obtain a predetermined detectionsensitivity.

On the other hand, when the wafer is free from the via b, no dischargeis caused between the objective lens system 724 and the wafer even ifthe electrodes 725 are applied with a voltage of +350, so that the waferW can be inspected for defects. In this event, since the secondaryelectrons are converged by the voltage applied to the electrodes 725 andfurther converged by the objective lens 724, the detector 761 withgreater efficiency detects the secondary electrons. Consequently, thewafer defect detector processing is performed at a higher speed, so thatthe inspection can be carried at a higher throughput.

Description of the Relationship Among Main Functions in the ProjectingMethod and its General View

A schematic general view of an inspection apparatus according to thepresent invention is shown in FIG. 11. However, some components areomitted for illustration.

In FIG. 11, the inspection apparatus has a primary column 71-1, asecondary column 71-2 and a chamber 32. An electron gun 721 is arrangedon the inside of the primary column 71-1, and a primary optical system72 is disposed along the optical axis of an electron beam (a primaryelectron beam) irradiated from the electron gun 721. Further, a stage 50is installed in the interior of the chamber 32 and a sample W is loadedon the stage 50.

On the other hand, in the interior of the secondary column 71-2, acathode lens 724, a numerical aperture NA-2, a Wien filter 723, a secondlens 741-1, a field aperture NA-3, a third lens 741-2, a fourth lens741-3 and a detector 761 are located on the optical axis of thesecondary electron beam emanating from the sample W. It is to be notedthat the numerical aperture NA-2 corresponds to an aperture diaphragm,which is a thin plate made of metal (Mo or the like) having a circularaperture formed therein. Herein, an aperture section is arranged so asto be at a focused location of the primary electron beam and also at afocusing location of the cathode lens 724. Accordingly, the cathode lens724 and the numerical aperture NA-2 construct a telecentric electronicoptical system.

On the other hand, the output from the detector 761 is input into acontrol unit 780, and the output from the control unit 780 is input intoa CPU 781. A control signal from the CPU 781 is input into a primarycolumn control unit 71 a, a secondary column control unit 71 b and astage driving mechanism 56. The primary column control unit 71 acontrols a lens voltage in the primary optical system 72, and thesecondary column control unit 71 b controls lens voltages in the cathodelens 724 and the second lenses 741-1 to the fourth lens 741-3 and alsoan electromagnetic field applied to the Wien filter 723.

Further, the stage driving mechanism 56 transmits position data of thestage to the CPU 781. Still further, the primary column 71-1, thesecondary column 71-2 and the chamber 32 are connected to the vacuumexhausting system (not shown) and exhausted by a turbo pump in thevacuum exhausting system so as for the interior thereof to be maintainedin vacuum.

-   (PRIMARY BEAM) The primary electron beam from the electron gun 721    enters into the Wien filter 723 while receiving a lens effect caused    by the primary optical system 72. Herein, L_(a)B₆ may be used for a    chip of the electron gun, which is a rectangular negative electrode    and from which a high current can be emitted. Further, the primary    optical system 72 may use an electrostatic (or electromagnetic)    quadrupole or octopole lens, asymmetric with respect to a rotating    axis. This lens, similar to what is called a cylindrical lens, can    cause a focusing and a divergence in the X and the Y axes    respectively. Such a configuration comprising two or three steps of    these lenses to optimize respective lens conditions allows the beam    irradiation region on the sample surface to be formed into a    rectangular or elliptical shape as desired without any loss of    irradiated electrons.

Specifically, in the case of the electrostatic lenses being used, fourcylindrical rods may be used. Each two opposite electrodes are made tobe equal in potential and reverse voltage characteristics are giventhereto.

It is to be appreciated that a lens formed in the shape of a quarter ofa circular plate used commonly in the electrostatic deflector, ratherthan the cylindrical shape, may be used for the quadrupole lens. Thatcase allows for the miniaturization of the lens. The primary electronbeam after passing through the primary optical system 72 is forced bythe deflecting effect from the Wien filter 723 so as to deflect thetrajectory thereof. In the Wien filter 723, the magnetic field iscrossed with the electric field at right angles, and only the chargedparticles satisfying the Wien condition of E=vB are advanced straightahead, and the orbits of the other charged particles are deflected,where the electric field is E, the magnetic field B, and the velocity ofthe charged particle v. A force FB by the magnetic field and anotherforce FE by the electric field may be generated against the primarybeam, and consequently the primary beam is deflected. On the other hand,the force FB and the force FE are reversely applied to the secondarybeam and those forces are cancelled to each other, so that the secondarybeam is allowed to go directly forward.

A lens voltage of the primary optical system 72 has been determinedbeforehand such that the primary beam is formed into an image at theaperture portion of the numerical aperture NA-2. That numerical apertureNA-2 prevents any excess electron beams to be dispersed in the apparatusfrom reaching to the sample surface and thus prevents charging orcontamination in the sample W. Further, since the numerical apertureNA-2 and the cathode lens 724 together form the telecentric electronicoptical system, the primary beams that have passed through the cathodelens 724 may turn to be parallel beams, which are irradiated uniformlyand similarly against the sample W. That is to say, it accomplishes whatis called in an optical microscope, the Koehler illumination.

-   (SECONDARY BEAM) When the primary bean is irradiated against the    sample, secondary electrons, reflected electrons or back-scattering    electrons are generated as the secondary beam from the beam    irradiated surface of the sample.

The secondary beam passes through the lens while receiving a lens effectfrom the cathode lens 724.

It is to be noted that the cathode lens 724 is composed of three piecesof electrodes. Among those electrodes, the one at the lowest position isdesigned to form a positive electric field between the potentials in thesample W side and itself, and to take in electrons (particularly,secondary electrons with smaller directivities) so that the electronsmay be efficiently introduced into the lens.

Further, the lens effect takes place in such a way that voltages areapplied to the first and the second electrodes of the cathode lens 724and the third electrode is held to zero potential. On the other hand,the numerical aperture NA-2 is disposed at the focal position of thecathode lens 724, that is, the back focal position with respect to thesample W. Accordingly, the trajectories of electron beams originatingfrom the center of the field of view (out of the axis) also become theparallel beams and pass through the central location in this numericalaperture NA-2 without being kicked out any further.

It is to be appreciated that the numerical aperture NA-2 serves toreduce lens aberrations of the second lens 741-1 to the fourth lens741-3 for the secondary beams. Those secondary beams having passedthrough the numerical aperture NA-2 may not affected by the deflectingeffect from the Wien filter 723 but may keep on going straight throughthe filter. It is to be noted that varying the electromagnetic fieldapplied to the Wien filter 723 may allow only electrons having specifiedenergies (for example, secondary electrons, reflected electrons orback-scattering electrons) to be introduced into the detector 761.

If the secondary beam is formed into an image only by the cathode lens724, the lens effect may be great and an aberration is more likely tooccur. Accordingly, the cathode lens 724 may be combined with the secondlens 741-1 to perform first image forming. The secondary beam can beformed into an intermediate image on the field aperture NA-3 by thecombination of the cathode lens 724 and the second lens 741-1. In thatcase, since typically the magnification required for the secondaryoptical system has often been insufficient, the third lens 741-2 and thefourth lens 741-3 are added in the configuration as the lenses formagnifying the intermediate image. The secondary beam is magnified andformed into an image by the third lens 741-2 and the fourth lens 741-3respectively, which means that the secondary beam is formed into animage three times in this case. It is to be noted that the beam may befocused only once by using both the third lens 741-2 and the fourth lens741-3 (a total of two times).

In addition, each of the second lens 741-1 to the fourth lens 741-3should be a lens symmetrical with respect to a rotating axis of the kindreferred to as a uni-potential lens or Einzell lens. Each lens iscomposed of three electrodes, in which typically the outer twoelectrodes have zero potentials and a voltage applied to the centerelectrode is used to causes a controlling lens effect. Further, thefield aperture NA-3 is located in the intermediate image forming point.The field aperture NA-3, which constrains the field of view to belimited to a required range, similar to a field stop in an opticalmicroscope, for the case of an electron beam, cooperatively blocks anyexcess beams with the subsequent stages of the third and the fourthlenses 741-2 and 741-3 so as to prevent charging and/or contamination ofthe detector 761. It is to be noted the magnification can be controlledby varying the lens conditions (the focal distances) of the third andthe fourth lenses 741-2 and 741-3.

The secondary beam is magnified and projected by the secondary opticalsystem and formed into an image on the detection plane of the detector761. The detector 761 comprises a MCP for amplifying an electron, afluorescent screen for converting the electrons into light, lenses andother optical elements for use as a relay and transmitting an opticalimage between the vacuum system and external components, and an imagesensor (CCD or the like). The secondary beam is formed into an image onthe MCP detection plane and amplified, and then the electrons areconverted into light signals by the fluorescent screen, which are inturn converted into photo-electric signals by the image sensor.

The control unit 780 reads out the image signal of the sample from thedetector 761 and transmits it to the CPU 781. The CPU 781 performs adefect inspection of the pattern by template matching and so forth fromthe image signal. On the other hand, the stage 50 is adapted to bemovable in the X and Y directions by a stage driving mechanism 56. TheCPU 781 reads the position of the stage 50 and outputs a drive controlsignal to the stage driving mechanism 56 to drive the stage 50, allowingfor sequential detection and inspection of the images.

Thus, in the inspection apparatus according to the embodiment, since thenumerical aperture NA-2 and the cathode lens 724 comprise thetelecentric electronic-optical system, therefore the primary beam may beirradiated uniformly against the sample. That is, it accomplishes theKoehler illumination.

Further, as to the secondary beam, since all of the principle beams fromthe sample W enter the cathode lens 724 at a right angle (parallel tothe optical axis of the lens) and pass through the numerical apertureNA-2, therefore the peripheral beam would not be kicked out thuspreventing deterioration of image brightness in the periphery of thesample. In addition, although a variation of the energy pertaining tothe electrons gives a different focal position, which causes what iscalled a magnification chromatic aberration (especially for thesecondary electrons, since the energies thereof are varied to a greatextent, the magnification chromatic aberration is rather great), thearrangement of the numerical aperture NA-2 at the focal position of thecathode lens 724 makes it possible to control the magnificationchromatic aberration so that it is kept low.

On the other hand, since a change of the magnification factor isexecuted after the beam has passed through the numerical aperture NA-2,any changes in the determined magnification factor in the lens conditionfor the third and the fourth lenses 741-2 and 741-3 can still bring auniform image over the field of view to be obtained in the detectionside. It should be appreciated that although an even and uniform imagecan be obtained in the present embodiment, typically, increasing themagnification may problematically cause deterioration in the brightnessof the image. Accordingly, in order to improve this problematiccondition, when the lens condition for the secondary optical system ischanged to vary the magnification factor, the lens condition for theprimary optical system should be controlled such that the effectivefield of view on the sample determined in association with themagnification and the electron beam to be irradiated on the sample maybe equally sized.

That means, as the magnification is increased, consequently the field ofview gets smaller, but when the irradiation beam current of the electronbeam is increased at the same time, the signal density of the detectedelectron can be kept at a constant level and the brightness of the imagemay be prevented from deterioration even if the beam is magnified andprojected in the secondary optical system.

Further, although in the inspection apparatus according to the presentembodiment, a Wien filter 723 has been employed, which deflects thetrajectories of a primary beam but allows a secondary beam to gostraight forward, the application is not limited to this and theapparatus may employ a Wien filter with another configuration in whichthe primary beam is allowed to go straight forward but the orbit of thesecondary beam is deflected. Still further, although in the presentembodiment, a rectangular cathode and a quadrupole element lens are usedto form a rectangular beam, the application is not limited to this and,for example, a rectangular beam or elliptical beam may be formed from acircular beam, or the circular beam may be passed through a slit toextract the rectangular beam.

Electrode

Between the objective lens 724 and the wafer W, there is disposed anelectrode 725 having a shape approximately symmetrical with respect tothe optical axis of irradiation of the electron beam. Typical shapes ofthe electrode 725 are shown in FIGS. 12 and 13.

FIGS. 12 and 13 are perspective views of the electrode 725, wherein FIG.12 is a perspective view of an electrode 725 with a cylindrical shapeformed to be axially symmetrical, while FIG. 13 is a perspective view ofanother electrode 725 with a disk-like shape formed to be axiallysymmetrical.

Although in this embodiment, the explanation is made for the case wherethe electrode 725 is cylindrical in shape as shown in FIG. 12, theelectrode may have a disk-like shape as shown in FIG. 13 so far as it isapproximately symmetrical with respect to the optical axis ofirradiation of the electron beam.

Further, in order to generate the field which is to prevent an electricdischarge between the objective lens 724 and the wafer W, apredetermined voltage (negative potential) lower than that applied tothe wafer W (the potential thereof is 0V since the wafer is grounded inthis embodiment) is applied to the electrode 725 by the power supply726. The potential distribution between the wafer W and the objectivelens 724 at this point in time will be described with reference to FIG.14.

FIG. 14 is a graph of the voltage distribution between the wafer W andthe objective lens 724.

In FIG. 14, the voltage distribution is shown over a range from thewafer W to the objective lens 724 along the optical axis of irradiationof the electron beam, indicating the position on the optical axis by thehorizontal axis.

The voltage distribution from the objective lens 724 to the wafer W forthe prior art with no electrode 725 is shown to vary gently from themaximum value of the voltage applied to the objective lens 724 to thewafer W that has been grounded (as shown with the thinner line in FIG.14).

In contrast, for the electron beam apparatus according to the presentinvention, since the electrode 725 is arranged between the objectivelens 724 and the wafer W, and further the electrode 725 is supplied witha predetermined voltage (negative potential) lower than that applied tothe wafer W from the power supply 726, the electric field of the wafer Wis weakened (as shown with the thicker line).

Therefore, with the electron beam apparatus of the present invention,the electric field could not be dense in the vicinity of the via b inthe wafer W, so that there is no strong electric field. Accordingly,even if there is an emission of secondary electrons emitted by theelectron beam irradiated onto the via b, these emitted secondaryelectrons would not be accelerated enough to ionize the residual gas, sothat electric discharge may be prevented between the objective lens 724and the wafer W.

Further, since electric discharge is prevented between the objectivelens 724 and the wafer W, there would be no damage to the pattern in thewafer W, which otherwise would be caused by an electric discharge.

On the other hand, although in the above embodiment, the electricdischarge can be prevented between the objective lens 724 and the waferW having the via b, the detection sensitivity of the detector 761 to thesecondary electrons may possibly decrease depending on the level of thenegative potential applied to the electrode 725. Accordingly, it issuggested that in the case of a decrease in the detection sensitivity, aseries of operations including the irradiation of the electron beam andthe detection of the secondary electrons should be repeated a pluralitytimes, and the obtained number of detection results are processed withan accumulative addition or averaging operation to obtain a desiredsensitivity (S/N ratio of the signal).

In the present invention, the detection sensitivity, for the purpose ofexplanation, is exemplarily defined as a signal to noise ratio (S/Nratio).

The above described operation for detecting secondary electrons will nowbe described with reference to FIG. 15.

FIG. 15 is a flow chart illustrating the operation for detectingsecondary electrons in the electron beam apparatus.

Primarily, the secondary electrons from the sample to be inspected aredetected by the detector 761 (Step 1). Then, a determination is made onwhether or not the signal to noise ratio (the S/N ratio) is equal to orgreater than a predetermined value (Step 2). At step 2, if the signal tonoise ratio is equal to or greater than the predetermined value, thenthe detecting operation by the detector 761 for the secondary electronsis determined to be sufficient, and the secondary electron detectingoperation is completed.

On the contrary, if the signal to noise ratio is lower than thepredetermined value at step 2, a series of operations comprising theirradiation of the electron beam and the detection of the secondaryelectrons is repeated 4N times and the results are averaged (Step 3). Atthat time, since the initial value for N has been set to “1”, thereforethe secondary electron detecting operation should be performed 4 timesfor the first time at step 3.

Then, N is incremented by “1” for counting up (Step 4), and again atstep 2 a determination is made on whether or not the signal to noiseratio is equal to or greater than the predetermined value. If the signalto noise ratio is again lower than the predetermined value, the processgoes to step 3 again, and this time, the detecting operation of thesecondary electrons should be repeated 8 mtimes. Then N is incrementedand the steps 2 to 4 should be repeated until the signal to noise ratiois equal to or greater than the predetermined value.

Further in this embodiment, although the explanation is given for thecase where the electric discharge to the wafer W having the via b may beeffectively prevented by applying to the electrode 725 a predeterminedvoltage (a negative potential) lower than that applied to the wafer 8,there would be another case where the detection sensitivity to thesecondary electrons is disadvantageously decreased.

Accordingly, if the sample to be inspected is a wafer having no vias orthe like, which is of a kind in which electric discharge is less likelyto occur between itself and the objective lens 724, then the voltageapplied to the electrode 725 may be controlled so that the efficiency ofdetection of secondary electrons can be increased.

Specifically, even in the case where the sample to be inspected isgrounded, a voltage applied to the electrode 725 may be set to apredetermined voltage higher than that applied to the sample to beinspected, for example, the voltage of +10 V. Further, at that time, thedistance between the electrode 725 and the sample to be inspected shouldbe determined to be enough that the electric discharge would not occurbetween the electrode 725 and the sample to be inspected.

In this case, the secondary electrons generated by the irradiation ofthe electron beam onto the sample to be inspected is accelerated towardthe side of the electron beam source 721 by the electric field generatedby the voltage applied to the electrode 725. Then, the secondaryelectrons are further accelerated by the electric field generated by thevoltage applied to the objective lens 724 toward the side of theelectron beam source 721 to be subject to the convergent effect,resulting in many electrons entering the detector 761, thus increasingthe detection efficiency.

Still further, since the electrode 725 is axially symmetrical, it alsoserves as a lens to converge the electron beam irradiated to the sampleto be inspected. Therefore, by controlling the voltage applied to theelectrode 725, the primary electron beam can be converged to benarrower. Further, since the primary electron beam can also be convergedto be narrower by way of the electrode 725, an objective lens systemhaving lower aberration can be constructed by means of the combinationof the objective lens 724 and the electrode 725. The electrode 725 maybe approximately axially symmetrical so long as such lens action can beobtained.

According to an electron beam apparatus of the subject embodiment, sincean electrode having a shape approximately symmetrical with respect tothe axis of irradiation of the electron beam has been arranged betweenthe sample to be inspected and the objective lens so as to control theelectric field intensity in the electron beam irradiated plane of thesample to be inspected, therefore the electric field between the sampleto be inspected and the objective lens can be controlled.

Further, since an electrode having a shape approximately symmetricalwith respect to the axis of irradiation of the electron beam has beenarranged between the sample to be inspected and the objective lens so asto weaken the electric field intensity in the electron beam irradiatedplane of the sample to be inspected, the electric discharge between thesample to be inspected and the objective lens can be eliminated.

Since there has been no modification such as decreasing the voltageapplied to the objective lens and therefore the secondary electrons cango through the objective lens efficiently, the detection efficiency canbe improved and a signal with good S/N ratio can be obtained.

Further, the voltage can be controlled so as to weaken the electricfield intensity in the electron beam irradiated plane of the sample tobe inspected, depending on the category of the sample to be inspected.

For example, if the sample to be inspected is of a type likely to causean electric discharge between the objective lens and itself, theelectric discharge can be prevented by weakening the electric fieldintensity in the electron beam irradiated plane of the sample to beinspected by changing the voltage applied to the electrode.

Further, the voltage applied to the electrode can be changed dependingon whether or not said semiconductor device has a via, that is, thevoltage applied in order to weaken the electric field intensity in theelectron beam irradiated plane of the semiconductor wafer can bechanged.

For example, if the sample to be inspected is of a type that is likelyto cause an electric discharge between the objective lens and itself,the electric discharge especially in the via or in the vicinity of thevia can be prevented by changing the electric field generated by theelectrodes, thereby weakening the electric field intensity in theelectron beam irradiated plane of the sample to be inspected.

Further, since the electric discharge is prevented between the via andthe objective lens, there would be no damage to the pattern or the likein the semiconductor wafer, which otherwise would be caused by theelectric discharge.

Further, since the potential applied to the electrode has been madelower than that applied to the sample to be inspected, the electricfield intensity in the electron beam irradiated plane of the sample tobe inspected can be weakened, thus preventing the electric discharge tothe sample to be inspected.

Yet further, since the potential applied to said electrode is a negativepotential and the sample to be inspected is grounded, the electric fieldintensity can be weakened in the electron beam irradiated plane of thesample to be inspected, thus preventing the electric discharge to thesample to be inspected.

Modified Embodiment of E×B Separator

FIG. 16 shows an E×B separator of an embodiment according to the presentinvention. FIG. 16 is a cross sectional view taken along a plane normalto an optical axis. Four pairs of electrodes 701 and 708, 702 and 707,703 and 706, and 704 and 705 used for generating an electric field aremade of a non-magnetic conductive material, together forming anapproximately cylindrical shape as a whole, and fixedly secured withscrews or the like (not shown) on an inner face of a cylinder 713 madeof insulating material for supporting the electrodes. An axis of thecylinder 713 for supporting the electrodes and an axis of the cylinderformed by the electrodes are made identical with the optical axis 716. Aplurality of grooves 714 is respectively arranged on the inner face ofthe electrode supporting cylinder 713 in parallel with the optical axis716 in each space between the electrodes 701, 702, 703, 704, 705, 706,707, and 708. Then, the inner face areas of said grooves are coated withconductive material 715, and are set to the ground potential.

Upon generating the electric field, if the voltages are appliedrespectively to the electrodes in such a manner that a voltageproportional to “cos θ₁” is applied to the electrodes 702 and 703, “−cosθ₁” to the electrodes 706 and 707, “cos θ₂” to the electrodes 701 and704, and “−cos θ₂” to the electrodes 705 and 708, there emerges anelectric field that has a uniform and parallel pattern over a regionequivalent to approximately 60% of the region within the inner diameterof the electrodes. FIG. 17 shows a simulation result for the electricfield distribution. It should be noted that although this example usesfour pairs of electrodes, even with three pairs of electrodes a uniformand parallel pattern of the electric field can be obtained for theregion equivalent to approximately 40% of the region within the innerdiameter.

The generation of the magnetic field is accomplished by placing tworectangular permanent magnets made of platinum alloy 709 and 710 inparallel outside the electrode supporting cylinder 713. Projections 712made of magnetic material are arranged in peripheral portions of thepermanent magnets 709 and 710 in the sides facing the optical axis 716.These projections 712 are arranged to compensate for the outwardlyconvex distortion of the lines of magnetic force in the sides facing theoptical axis 716, and the size and shape of the projection may bedetermined based on the simulation analysis.

The exterior of the permanent magnets 709 and 710 is provided with amagnetic circuit 711 made up of ferromagnetic material so that thepassage for the lines of magnetic force by the permanent magnets 709 and710 in the opposite side to the optical axis 716 is formed to be acylindrical shape that is coaxial with the electrode supporting cylinder713.

The E×B separator as shown in FIG. 16 is also applicable to a scanningtype electron beam inspection apparatus as well as a projective electronbeam inspection apparatus as shown in FIG. 8.

As is apparent from the above description, according to the subjectembodiment, both the electric field and the magnetic field are allowedto emerge uniformly in the larger region around the optical axis, sothat even if the area exposed to the irradiation of the primary electronbeam is extended, the aberration for the image passed through the E×Bseparator would fall into a reasonable range of values.

Since the projections have been arranged in the peripheral portions ofthe magnetic poles generating the magnetic field, and also said magnetpoles are arranged outside of the electrodes for generating the electricfield, it allows a uniform magnetic field to be generated and distortionby the magnetic poles to be reduced. Further, since the magnetic fieldhas been generated by use of the permanent magnets, the E×B separatorcan be fully installed in a vacuum. Still further, the electrodes forgenerating the electric field and the magnetic circuit for forming themagnetic path have been formed into coaxial cylindrical shapes centeredon the optical axis, which makes it possible to reduce in size the E×Bseparator as a whole.

Precharge Unit

The precharge unit 81, as illustrated in FIG. 1, is disposed adjacent tothe column 71 of the electron-optical system 70 within the workingchamber 31. Since this inspection apparatus is configured to inspectdevice patterns or the like formed on the surface of a substrate or awafer to be inspected by irradiating the wafer with an electron beam, sothat the secondary electrons generated by the irradiation of theelectron beam are used as information on the surface of the wafer.However, the surface of the wafer may be charged up depending onconditions such as the wafer material, energy of the irradiatedelectrons, and so on. Further, on the surface of a single wafer, someregions may be highly charged, while other regions may be lightlycharged. Variations in the amount of charge on the surface of the wafercause corresponding variations in information provided by the resultingsecondary electrons, thereby failing to provide correct information. Forpreventing such variations, in this embodiment, the precharge unit 81 isprovided with a charged particle irradiating unit 811. Before electronsfor inspection are irradiated to a predetermined region on a wafer to beinspected, charged particles are irradiated from the charged particleirradiating unit 811 of the precharge unit 81 to eliminate variations incharge. The charges on the surface of the wafer may be detected bypreviously forming an image of the surface of the wafer to be inspected,and by evaluating the image, and the precharge unit 81 can be operatedbased on such detection.

Alternatively, the precharge unit 81 may be operated while blurring theprimary electron beam.

FIG. 18 shows the main components of a precharge unit of an embodimentaccording to the present invention.

Charged particles 818 from a charged particle irradiation source 819 areaccelerated with a voltage determined by a bias supply 820 so as to beirradiated onto a sample substrate W. An inspecting region 815, and aregion 816 as well, are indicated as locations that have been alreadyexposed to the charged particle irradiation for a pre-treatment, and theregion 817 is indicated as a location which is currently exposed to thecharged particle irradiation. In this drawing, although the samplesubstrate W is shown to be scanned in the direction indicated with anarrow, another charged particle beam source 819 may be arranged on theopposite side to the first electron beam source as shown with the dottedline in the drawing, so that the charged particle beam sources 819 and819 may be alternately turned on and off in synchrony with the directionof the scanning of the sample W. In this case, if the energy of thecharged particles is too high, the secondary electron 712 yield from aninsulating portion of the sample substrate W would exceed 1, thuscausing the surface to be positively charged, and even a yield of notmore than 1 would still make the phenomenon complicated with thegenerated secondary electrons thus decreasing the irradiation effect,and accordingly, it is preferred that the voltage for the energy of thecharged particles should be set to a landing voltage of 100 eV or lower(preferably higher than 0 eV and lower than 30 eV), which cansignificantly reduce the generation of the secondary electrons.

FIG. 19 shows a second embodiment of a precharge unit of the presentinvention. FIG. 19 shows an irradiation source of such type thatirradiates an electron beam as a charged particle beam. The irradiationsource comprises a hot filament 821, a deriving electrode 824, a shieldcase 826, a filament power supply 827, and an electron deriving powersupply 823. The deriving electrode 824 is 0.1 mm in thickness, has aslit 0.2 mm wide and 1.0 mm long, and is arranged relative to thefilament 821 of a diameter of 0.1 mm so as to take the form of athree-electrode type electron gun. The shield case 826 is also providedwith a slit of 1 mm wide and 2 mm long, and is assembled so that theshield case 826 is spaced from the deriving electrode 824 by 1 mm withits slit center being aligned with the slit center of the derivingelectrode 824. The filament is made of tungsten (W), and it is foundthat an electron current of in the order of μA can be obtained with acurrent of 2 A being supplied to the filament when a deriving voltage of20 V and a bias voltage of −30 V are applied.

The example has been shown for illustrative purposes only and thefilament may be made of other materials, for example, a high meltingpoint metal such as Ta, Ir, Re or the like, thoria-coated W, or an oxideelectrode, and in this case, needless to say, the filament currentshould be varied depending on the material, the line diameter and theline length to be used. Further, other kinds of electron guns may beused as long as the electron beam irradiated area, the electron currentand the energy can be respectively set to appropriate value.

FIG. 20 shows a third embodiment of a precharge unit of the presentinvention. FIG. 20 shows an irradiation source of a type that irradiatesions 829 as a charged particle beam. This irradiation source comprises afilament 821, a filament power supply 822, an electric discharge powersupply 827, and an anode shield case 826, in which both of anode 828 andthe shield case 826 have the same sized slit of 1 mm×2 mm respectivelyformed therethrough, and they are assembled so that the centers of bothslits are aligned with each other. Ar gas 830 is introduced into theshield case 826 through a pipe 831 with about 1 Pa and this irradiationsource is operated by way of an arc discharge caused by the hot filament821. The bias voltage is set to a positive value.

FIG. 21 shows a plasma irradiation type of a fourth embodiment of aprecharge unit according to the present invention. It has the samestructure as that of FIG. 20. The operation thereof, similarly to theabove description, is made effective by way of the arc discharge by thehot filament 821, in which by setting the bias potential to 0V, theplasmas 832 are forced by gas pressure to effuse through the slit to beirradiated onto a sample substrate. Since in the plasma irradiationmethod, the beam is composed of a group of particles that has bothpositive and negative charges, which is different from the otherirradiation methods, it allows both positive and negative surfacepotentials in the surface of the sample substrate to approach zero.

A charged particle irradiating section 819 arranged in the proximity ofthe sample substrate W has a configuration as illustrated in any ofFIGS. 18 to 21, which is designed to irradiate charged particles 818onto the sample substrate with a suitable condition depending on thedifference in the surface structure, e.g., silicon dioxide film orsilicon nitride film, of the sample W, or depending on a differentrequirement for each sample substrate after respective differentprocesses, and in which after performing the irradiation to the samplesubstrate under the optimal irradiation condition, that is, aftersmoothing the potential in the surface of the sample substrate W orsaturating the potential therein with the charged particles, an image isformed by the electron beam 711 and 712 to be used to detect anydefects.

As described above, since according to the subject embodiment,pre-treatment by means of charged particle irradiation is employed justbefore measurement and thereby an evaluated image distortion by thecharging would not occur or would be neglible, any defects can beaccurately detected.

Further, according to the embodiment according to the present invention,since a high current is allowed to be used for scanning a stage by anamount that has caused problems in the prior art, a large number ofsecondary electrons can be detected and a detection signal having a goodS/N ratio can be obtained, thus improving the reliability of defectdetection.

Still further, with a larger S/N ratio, faster scanning of the stagestill can produce good image data, thus allowing inspection throughputto be greater.

FIG. 22 schematically shows an imaging apparatus equipped with aprecharge unit according to the present embodiment. The imagingapparatus comprises a primary optical system 72, a secondary opticalsystem 74, a detecting system 76 and an electric charge control means840 for uniforming a distribution or reducing a potential level ofelectric charge residing on an object. The primary optical system 72 isan optical system for irradiating an electron beam or a charged particlebeam against the surface of an object to be inspected (hereafterreferred to as an object) “W”, and comprises: an electron gun 721 foremitting the electron beam; electrostatic lenses 722 for respectivelyfocusing and contracting a primary electron beam 711 emitted from theelectron gun 721; a Wien filter or an E×B separator 723 for deflectingthe primary electron beam so that the optical axis thereof may be normalto the surface of the object; and electrostatic lenses 724 forrespectively focusing and magnifying the electron beam, wherein thosecomponents are arranged in the order as illustrated in FIG. 22, with theelectron gun 721 being disposed in the topmost location and the opticalaxis of the primary electron beam 711 emitted from the electron gunbeing inclined with respect to the line normal to the surface of theobject W (i.e., the sample surface). The E×B deflecting system 723comprises an electrode 723-1 and a magnet 723-2.

The secondary optical system 74 comprises electrostatic lenses 741 eachdisposed above the E×B deflecting system 723 of the primary opticalsystem. The detecting system 76 comprises a combination 751 of ascintillator and a micro-channel plate (MCP) for converting a secondaryelectron 712 into an optical signal, a CCD 762 for converting theoptical signal into an electric signal, and an image processing unit763. The structures and functions of these components in theabove-mentioned primary optical system 72, secondary optical system 74and detecting system 76 are all similar to those according to the priorart, and detailed description thereof will be omitted.

In this embodiment, an electric charge control means 840 for uniforminga distribution or reducing the potential level of electric chargeresiding on an object comprises an electrode 841 disposed in proximityto the object W between the object W and the electrostatic deflectinglens 724 of the primary optical system 72 located most closely to theobject W, a change-over switch 842 electrically connected to theelectrode 841, a voltage generator 844 electrically connected to oneterminal 843 of the change-over switch 842, an electric charge detector846 electrically connected to the other terminal 845 of the change-overswitch 842. The electric charge detector 846 has a high level ofimpedance. The electric charge reducing means 840 further comprises agrid 847 disposed between the electron gun 721 and the electrostaticlens 722 of the primary optical system, and a voltage generator 848electrically connected to the grid 847. A timing generator 849 functionsto give commands on the operational timings to the CCD 762 and the imageprocessing unit 763 of the detecting system 76, and the change-overswitch 842, and the electric charge detectors 846 and 848 of theelectric charge reducing means 840.

The operation of the electron beam apparatus with the aboveconfiguration will now be described.

A primary electron beam 711 emitted from the electron gun 721 passestrough the electrostatic lenses 722 of the primary optical system 72 andreaches up to the E×B deflecting system 723, where the beam 711 isdeflected to be normal to the surface of the object W by the E×Bdeflecting system 723, and then further goes through the electrostaticdeflectors 724 to be irradiated onto the surface (the objective surface)WF of the object W. The secondary electrons emanate from the surface WFof the object W depending on the properties of the object. Thissecondary electrons 712 are sent to the combination of scintillator andMCP 751 of the detecting system 76 via the electrostatic lenses 741 ofthe secondary optical system 74 and converted into light by thescintillator, which light is photo-electrically converted by the CCD762, and the converted electric signal is used by the image processingunit 763 to form a two dimensional image (having a gradation). It is tobe appreciated that, in any typical inspection apparatus of this kind,the primary electron beam to be irradiated against the object is adaptedto be irradiated onto the objective surface WF covering all of thedesired locations so as to collect data on that objective surface eitherby performing a scanning operation with the primary electron beam by theknown deflecting means (not shown), by moving a table T carrying theobject thereon in the two dimensional directions X and Y, or by thecombination of those movements.

The primary electron beam 711 irradiated onto the object W electrifiesthe object W on the vicinity of the surface thereof to be positivelycharged. As a result, the secondary electrons 712 emanating from thesurface WF of the object W are forced by Coulomb forces associated withthis electric charge to change their trajectory thereof depending on thecondition of the electric charge. This results in a distortion occurringin the image formed in the image processing unit 763. Since the electriccharging of the objective surface WF depends on the properties of theobject W, therefore in the case of a wafer having been employed as theobject, the electric charging of the surface is not necessarily the sameeven on the same wafer and further it is variable as time passes.Accordingly, there might be a risk of error in detection when the twopatterns in the different two locations on the wafer are compared.

In this viewpoint, in the embodiment of the present invention, theelectric charge detector 846 having a high level of impedance utilizesan idle time after the CCD 762 of the detecting system 76 has capturedan image for one scanning in order to measure the amount of the electriccharge of the electrode 841 located in the proximity of the object W.Then the power source 844 is invoked to generate a voltage sufficient toirradiate electrons corresponding to the measured amount of electriccharge, and after measurement the change-over switch 842 is actuated toconnect the electrode 841 to the power source 844, so that the voltagegenerated by the power source 844 may be applied to the electrode 841 tooffset the potential level of the charging. This prevents the distortionfrom occurring in the image formed in the image processing unit 763.Specifically, while a regular voltage is applied to the electrode 841, afocused electron beam may be irradiated against the object W, and incontrast once another voltage is applied to the electrode 841, whichcauses the focusing condition to vary greatly, an irradiation may becarried out with smaller current density covering a wide area expectedto be charged, so as to neutralize the positive charging on the objectand to thereby uniform the potential of the wide area expected to becharged to a specific positive(or negative) value or the potential ofthe wide area is reduced to a lower positive(or negative) value(including 0V) by uniforming and reducing the positive charging on theobject. Such an offset operation as described above may be carried outfor each scan.

The Whehnelt electrode or the grid 847 has the function of stopping theelectron beam to be irradiated from the electron gun 721 during thetiming of the idle time so as to stably carry out measurement of thecharging amount as well as the offset operation of the charging. Thetimings for the above-described operations may be commanded by thetiming generator 849, which are illustrated in the timing chart of FIG.23. It is to be noted that since the charging amount may be varieddepending on the locations in the case of a wafer being used as anobject, a plurality of groups composed of the electrodes 841, thechange-over switches 842, the voltage generators 844 and the electriccharge detectors 846 may be arranged along a scanning direction so as tosubdivide the area on the object and to accomplish control with muchhigher precision.

According to the embodiment according to the present invention of theinvention, the following effects may be expected to obtain:

(A) distortion in an image caused by the charging may be reduced with noregard to the properties of an object to be inspected;

(B) since idle time between the timings for the conventional measurementis used to execute the uniforming and offsetting of the charging, therewill be no effect on throughput;

(C) since real-time processing becomes possible, a time for anypost-processing, a memory and the like are no longer necessary; and,

(D) fast and highly accurate observation of an image and detection ofdefects may be accomplished.

FIG. 24 shows a general configuration of a defect inspection apparatusequipped with a pre-charge unit according to another embodiment of thepresent invention. The defect inspection apparatus comprises: anelectron gun 721 for emitting a primary electron beam; an electrostaticlens 722 for deflecting the emitted primary electron beam to beappropriately formed; a sample chamber 32 capable of being evacuated tovacuum by a pump(not shown); a stage 50 disposed in the sample chamberand capable of being moved in a horizontal plane with a sample such as asemiconductor wafer W or the like loaded thereon; an electrostatic lens741 of a projecting system for projecting at a specified magnification asecondary electron beam emanated from the wafer W and/or a reflectedelectron beam caused by an irradiation of the primary electron beamthereto, thereby forming an image; a detector 770 for detecting a formedimage as a secondary electron image of the wafer W; and a controlsection 1016 for performing a processing of detecting a defect in thewafer W based on the secondary electron image detected by the detector770 as well as for controlling the overall apparatus. It is to beappreciated that the above-described secondary electron image includes acontribution not only from the secondary electrons but also from thereflected electrons, though herein it is only referred to as thesecondary electron image.

Further, in the sample chamber 32, there is provided an UV lamp 1111mounted above the wafer W, which emits a beam of light in a wave lengthrange including ultra-violet ray. A glass surface of the UV lamp 1111 iscoated with a photoelectron emission material 1110 for emitting aphotoelectron “e⁻” resulting from photoelectric effect caused by thebeam emitted from the UV lamp 1111. Any light source may be employed forthe UV lamp 1111 so far as it can emit a beam in a wave length rangecapable of causing the photoelectron emission material 1110 to emit thephotoelectrons. Generally, it is advantageous from a viewpoint of costto employ a low-pressure mercury lamp capable of emitting ultra-violetray of 254 nm wave length. Further, the photoelectron emission material1110 may be selected from any arbitrary metals as far as it has anability to emit photoelectrons and, for example, “Au” may be preferable.

The above-described photoelectron has energy lower than that of theprimary electron beam. Herein, the lower energy means the energy in theorder of some eV to some ten eV, preferably 0 eV−10 eV. The presentinvention may employ any arbitrary means for generating those electronshaving such lower energy. For example, the present invention may beaccomplished also by employing a lower energy electron gun (not shown),in place of the UV lamp 1111.

Further, the defect inspection apparatus of the present embodimentcomprises a power supply 1113. A cathode of the power supply 1113 isconnected to the photoelectron emission material 1110, while a positivepole thereof is connected to the stage 50. Therefore, a negative voltageis applied to the photoelectron emission material 1110 with respect to avoltage applied to the stage 50 and thus the wafer W.

The detector 770 may have any arbitrary configuration so far as it canconvert the secondary electron image formed by the electrostatic lens741 into a signal that can be treated in a subsequent process. Forexample, as shown in detail in FIG. 46, the detector 770 may comprise amulti-channel plate 771, a fluorescence screen 772, a relay lens system773, and an imaging sensor 774 composed of multiple CCD elements. Themulti-channel plate 771 includes a large number of channels in the plateand generates more electrons while the secondary electrons formed intoan image by the electrostatic lens 741 are passing through saidchannels. That is, the multi-channel plate 771 increase the number ofthose secondary electrons. The fluorescence screen 772 converts thesecondary electrons into light by emitting fluorescence with theamplified secondary electrons. The relay lens system 773 guides thisfluorescence to the CCD imaging sensor 774, and then the CCD imagingsensor 774 converts an intensity distribution of the secondary electronson the surface of the wafer W into an electric signal for each element,namely, digital image data, which is, in turn, output to the controlsection 1016.

The control section 1016 may be composed of a general purpose personalcomputer or the like, as shown in FIG. 24. This computer may comprise acontrol section main body 1014 for executing various controls andoperations according to a predetermined program, a CRT 1015 fordisplaying a processed results from the main body 1014, and an inputsection 1018, such as a keyboard and a mouse, for an operator to input acommand; and of course, the computer may have a control section 1016that is composed of hardware or a workstation exclusively tailored for adefect inspection apparatus.

The control section main body 1014 comprises a CPU, a RAM, a ROM, a harddisk, and various control substrates including a video substrate(notshown). A secondary electron image storage region 1008 has beenallocated memory such as the RAM or the hard disk, for storing theelectric signal received from the detector 770, that is, the digitalimage data of the secondary electron image of the wafer W. Further, thehard disk contains, in addition to a control program for controlling theoverall defect inspection apparatus, a defect detection program 1009stored therein for reading out the secondary electron image data fromthe storage region 1008 and automatically detecting any defects in thewafer W based on said image data according to a specific algorithm. Thedefect detection program 1009 may have, for example, a function forcomparing an inspection spot on the wafer W to another inspection spoton the same wafer 5 and giving the operator a warning by displaying as adefect a pattern different from those patterns at a majority of otherinspection spots. Further, the secondary electron image 1017 may bedisplayed on the display section of the CRT 1015, so that the defect onthe wafer W may be detected by the operator's visual observation.

An operation of the electron beam apparatus according to the embodimentaccording to the present invention of the present invention will now bedescribed with reference to the flow chart shown in FIG. 27.

At first, the wafer 5, an object to be inspected, is set on the stage 50(Step 1200). This may be conducted in such a manner whereby a pluralityof wafers W contained in a loader (not shown), is set onto the stage 50one-by-one. Then, the electron gun 721 emits a primary electron beam,which passes through the electrostatic lens 722 and is irradiated onto aspecified inspection region on the set wafer W (Step 1202). Thesecondary electrons and/or reflected electrons (hereafter, referred toas “secondary electron”) emanate from the wafer W having been irradiatedwith the primary electron beam, and resultantly the wafer W is chargedup with positive potential. Then, those emanated secondary electrons areformed into an image on the detector 770 at a predeterminedmagnification through the electrostatic lens 741 of a magnifiedprojection system (Step 1204). At that time, while a negative voltage isbeing applied to the photoelectron emission material 1110 by the stage50, the UV lamp 1111 is turned on (Step 1206). As a result, anultra-violet ray with a vibration frequency of “ν” emitted from the UVlamp 1111 actuates the photoelectron emission material 1110 to emit aphotoelectron therefrom according to its energy quantum “hν” (where, “h”is the Planck's constant). Those photoelectrons, “e⁻”s, are irradiatedfrom the negatively charged photoelectron emission material 1110 towardthe positively charged-up wafer W so as to electrically neutralize saidwafer W. Thus, the secondary electron beam is allowed to form an imageon the detector 770 without being substantially affected by thepotential of the wafer W, which is otherwise possibly charged-up to bepositive.

In this way, the detector 770 detects an image of the secondary electronbeam that has emanated from the electrically neutralized wafer W withthe reduced image disorders, and converts it into digital image data tooutput (Step 1208). Then, the control section 1016, according to thedefect detection program 1009, executes a defect detection processing ofthe wafer W based on the detected image data (Step 1210). In this defectdetection processing, the control section 1016 may extract any defectiveportions by comparing each detected images which has been detected foreach of dies to one another, as described above, in the case of thewafer having a large number of equivalent dies. The control section 1016may make a comparison to inspect any matching between a referencesecondary electron beam image stored in the memory for a wafer having nodefects and an actually detected secondary electron beam image, toenable automatic detection of the defective portion. At that time, thedetected image may be displayed on the CRT 1015 with a mark indicating aportion that has been determined as a defective portion so that theoperator can make a final inspection to determine whether or not thewafer W actually has a defect. A specific example of this defectinspection method will be described later in detail.

If the result of the defect inspection processing at Step 1210 indicatesthat a defect exists in the wafer W (Step 1212, affirmativedetermination), the operator is informed by a warning of the defectexisting (Step 1218). As for the way of warning, for example, a messagenotifying the existence of the defect may be indicated on the displaysection of the CRT 1015, or additionally an enlarged image 1017 of thepattern in which the defect exists may be displayed thereon. Such adefective wafer may be immediately taken out of the sample chamber 32 soas to be stored in a different storage separate from the wafers with nodefect (Step 1219).

If the result of the defect inspection processing at Step 1210 indicatesthat no defect exists in the wafer W (Step 1212, negativedetermination), it is determined whether or not there are still anyremaining regions to be inspected (Step 1214). If some regions to beinspected still remain (Step 1214, affirmative determination), then thestage 50 is driven to move the wafer W so that the region to be furtherinspected may be positioned within the irradiative range of the primaryelectron beam (Step 1216). After that, the process goes back to Step1202 to repeat the same procedure for the other regions.

If no more regions to be further inspected remain (Step 1214, negativedetermination), or the process of taking out the defective wafer (Step1219) has been carried out, it is determined whether or not a wafer W,which is the current object to be inspected, is the last wafer, that isto say, whether or not any wafers remain in the loader (not shown) (Step1220). If the current wafer is not the last one (Step 1220, negativedetermination), the wafer that has already been inspected is stored in aspecified storage and a new wafer that has not been inspected yet is setinstead on the stage 50 (Step 1222). After that, the process goes backto the Step 1202 to repeat the same procedures for that wafer. Incontrast, if the current wafer is the last one to be inspected (Step1220, affirmative determination), the wafer that has already beeninspected is stored in the specified storage to complete the wholeprocess.

The UV photoelectron irradiation (Step 1206) may be performed at anyarbitrary timing and for any arbitrary period so far as it can helpprevent positive charging in the wafer W and detecting the secondaryelectron image with the image disorders having been reduced (Step 1206).While the process of FIG. 27 is repeated, the UV lamp 1111 may be kepton, or otherwise the turning on and off of the UV lamp 1111 may berepeated periodically in a cycle specified for each wafer. In the lattercase, an typical timing of the illumination, in addition to that shownin FIG. 27, may be before the secondary electron beam is formed into animage (Step 1204), or the illumination may begin before the primaryelectron beam is irradiated (Step 1202). Preferably, the UVphotoelectron irradiation should be continued at least during thesecondary electron detection, but the irradiation of the UVphotoelectrons may be stopped even before or during the secondaryelectron detection so far as the wafer has been sufficientlyneutralized.

A specific example for the defect inspection method at Step 1210 isshown in FIGS. 28( a) to 28(c). FIG. 28( a) shows an image 1231 for adie and an image 1232 for another die, which have been detected firstand second respectively. If an image for another die, which has beendetected third, is evaluated to be similar to the first image 1231, aportion 1233 of the second die image 1232 is determined to have adefect, and thus the defective portion can be detected.

FIG. 28( b) shows an example for measuring a line width of a patternformed on a wafer. The reference numeral 1236 designates an intensitysignal of an actual secondary electron in the scanning of an actualpattern 1234 along the direction 1235, and a width 1238 indicative of aportion where said signal continuously exceeds a threshold level 1237,which has been determined in advance by calibration, is measured as theline width of the pattern 1234. If any line width of the patternmeasured in this way does not fall within a predetermined range, thenthat pattern may be determined to have a defect.

FIG. 28( c) shows an example for measuring a potential contrast of apattern formed on a wafer. In the configuration shown in FIG. 24, anaxially symmetrical electrode 1239 has been provided above the wafer W,and to the electrode 1239 has been applied, for example, a potential of−10V relative to a wafer potential of 0V. At that time, an equipotentialsurface is assumed to be drawn in the shape as indicated by 1240. It isto be assumed herein that patterns 1241 and 1242 are at the potentialsof −4V and 0V respectively. In this case, since a second electronemanated from the pattern 1241 has an upward velocity equivalent to thekinetic energy of 2 eV in the −2V equipotential surface 40, the secondelectron overcomes that potential barrier 1240 and escapes from theelectrode 1239 as indicated by an trajectory 1243, which would bedetected by the detector 770. On the other hand, a second electronemanated from the pattern 1242 can not overcome the potential barrier of−2V and is driven back to the wafer surface as indicated by an orbit1244, which would not be detected. Accordingly, a detected image for thepattern 1241 appears to be brighter, while the detected image for thepattern 1242 appears to be darker. Thus the potential contrast can beobtained. If the brightness and potential for a detected image has beencalibrated in advance, a potential of a pattern can be measured from thedetected image. Further, based on that potential distribution, thepattern can be evaluated on any defective portions.

FIG. 25 shows a general configuration of a defect inspection apparatusequipped with a pre-charge unit according to a further embodiment of thepresent invention. It should be noted that components similar to thosein the embodiment of FIG. 24 are designated by the same referencenumerals, and a detailed description thereof will be omitted.

In this embodiment, as shown in FIG. 25, a glass surface of an UV lamp1111 is not coated with a photoelectron emission material. Instead, aphotoelectron emission plate 1110 b is disposed in a sample chamber 32above a wafer W, and the UV lamp 1111 is located in such a position thatthe radiated ultra-violet ray is irradiated onto the photoelectronemission plate 1110 b. The photoelectron emission plate 1110 b isconnected with a cathode, while a stage 50 is connected with a positivepole of a power supply 1113. The photoelectron emission plate 1110 b maybe made of metal such as Au or the like, or may be a plate coated withsuch metals.

An operation in the embodiment shown in FIG. 25 is similar to that inthe embodiment shown in FIG. 24. Since the embodiment of FIG. 25 alsoallows the photoelectrons to be irradiated onto a surface of a wafer W,a similar effect to that in the embodiment of FIG. 24 may be obtained.

FIG. 26 shows a general configuration of a defect inspection apparatusequipped with a pre-charge unit according to a still further embodimentof the present invention. It should be noted that components similar tothose in the embodiments of FIGS. 24 and 25 are designated by the samereference numerals, and a detailed explanation on those components willbe omitted.

In this embodiment, as shown in FIG. 26, a transparent window member1112 is arranged in a side face wall of a sample chamber 32, and a UVlamp 1111 is located outside the sample chamber 32 so that theultra-violet ray emitted from the UV lamp 1111 may pass through thewindow member 1112 and is irradiated onto a photoelectron emission plate1110 b disposed above a wafer W in the sample chamber 32. In theembodiment shown in FIG. 26, since the UV lamp 1111 is located externalto the sample chamber 32, which would be made vacuous, there is no moreneed to consider the resistivity of the UV lamp 1111 to the vacuum, thusgiving more selections for the UV lamp 1111 than the first and thesecond embodiments.

Other operations in the embodiment of FIG. 26 are similar to those inthe embodiments shown in FIGS. 24 and 25. Again, the embodiment of FIG.26 allows the photoelectrons to be appropriately irradiated onto asurface of the wafer W, and a similar effect to those in the embodimentof FIG. 24 or 25 may be exhibited.

Although the present invention described above takes some preferredembodiments as examples, the defect inspection apparatus equipped withthe pre-charge unit of the present invention is not limited to thoseembodiments described above, but may be arbitrarily and preferablymodified within the scope of the subject matter of the presentinvention.

For example, although a wafer W has been selected as an example of asample to be inspected, the sample to be inspected in the presentinvention is not limited to a wafer, and any object to which theelectron beam is applicable in detecting a defect may be selected as thesample. For example, a mask, on which an exposing pattern for the waferhas been formed, or the like may be an object to be inspected.

Further, although typical configurations for the electron beam apparatusused in the defect inspection are illustrated in FIGS. 24 to 26, theelectron optical system and others may be arbitrarily and preferablymodified. For example, although the electron beam irradiation system(721, 722) of the defect inspection apparatus shown in FIGS. 24 to 26employs a configuration in which the primary electron beam is irradiatedto enter a surface of the wafer W from diagonally above, a deflectionmeans for the primary electron beam may be arranged beneath theelectrostatic lens 741 so that the primary electron beam enters thesurface of the wafer W at right angles. As for such a separator, forexample, a Wien filter may be used, which deflects the primary electronbeam by an E×B field where an electric field and a magnetic field crossat right angles.

Further, it is apparent that any arbitrary means, other than thecombination of the UV lamp 1111 with the photoelectron emission material1110 or with the photoelectron emission plate 1110 b shown in FIGS. 24to 26, may be used as a means for emitting a photoelectron.

Still further, a process flow is not limited to that illustrated in FIG.27. For example, although a sample in the above embodiment, which hasalready been determined to be defective at Step 1212, would not havebeen further inspected for other regions on the sample, the flow may bechanged so that the defect may be detected through the inspectioncovering all regions. Further, if an irradiative region of the primaryelectron beam is extended so that one irradiation operation can coverall the inspection regions on a sample at once, Steps 1214 and 1216 maybe omitted.

Further, although in FIG. 27, when a wafer has been determined to have adefect at Step 1212 and the warning has been immediately given to theoperator to indicate the existence of the defect on the wafer at Step1218 requesting that it be dealt with in the subsequent process (Step1219), the flow may be changed so that a defect information may berecorded once and after a batch processing has been completed (i.e.,after the affirmative determination at Step 1220), the defectinformation on a defective wafer may be reported.

As explained in detail above, according to the defect inspectionapparatus and the defect inspecting method of the embodiments shown inFIGS. 24 to 26, since the electrons having energy lower than that of theprimary electron beam are supplied to the sample to be inspected,positive charging in the surface of the sample possibly caused by thesecondary electron emanation may be reduced, and thereby an imagedisorder of the secondary electron beam resulting from the charging maybe also resolved, and eventually such an advantageous effect can beobtained that the sample may be inspected for a defect with highaccuracy.

Further, according to the device manufacturing method which adopted thedefect inspection apparatus of the embodiments shown in FIGS. 24 to 26,since the defect inspection is conducted by using such the defectinspection apparatus as described above, other significant effects maybe obtained; that is, the yield of the product can be improved and thedelivery of defective products can also be prevented.

Potential Applying Mechanism

Referring next to FIG. 29, the potential applying mechanism 83 applies apotential of ± several volts to a carrier of a stage, on which the waferis placed, to control the generation of secondary electrons based on thefact that the secondary electron information or data emitted from thewafer (secondary electron generating rate) depend on the potential onthe wafer. The potential applying mechanism 83 also serves to deceleratethe energy originally possessed by irradiated electrons to provide thewafer with irradiated electron energy of approximately 100 mto 500 eV.

As illustrated in FIG. 29, the potential applying mechanism 83 comprisesa voltage applying device 831 electrically connected to the carryingsurface 541 of the stage device 50; and a charging examining/voltagedetermining system (hereinafter referred to as examining/determiningsystem) 832. The examining/determining system 832 comprises a monitor833 electrically connected to an image forming unit 763 of the detectingsystem 76 in the electron-optical system 70; an operator 834 connectedto the monitor 833; and a CPU 835 connected to the operator 834. The CPU835 supplies a signal to the voltage applying device 831.

The potential applying mechanism 83 is designed to find a potential atwhich the wafer to be inspected is hardly charged, and to apply suchpotential to the carrying surface 541.

In a method for inspecting for an electrical defect on a sample to beinspected, the defect on the portion which is designed to beelectrically insulated can be detected based on the fact that there is avoltage difference therein between the normal case where the portion isinsulated and the defective case where the portion is in a conductivecondition.

In this method, at first the electric charges are applied to the samplein advance, so that a voltage difference is generated between thevoltage in the portion essentially insulated electrically and thevoltage in another portion which is designed to be electricallyinsulated but is in a conductive condition due to the existence of anydefects, then the beam of the present invention is applied thereto toobtain data about the voltage difference, which is then analyzed todetect the conductive condition.

Beam Calibration Mechanism

Referring next to FIG. 30, the electron beam calibration mechanism 85comprises a plurality of Faraday cups 851, 852 for measuring a beamcurrent, disposed at a plurality of positions in a lateral region of thewafer carrying surface 541 on the turntable 54. The Faraday cups 851 areprovided for a narrow beam (approximately φ2 μm), while the Faraday cuts852 for a wide beam (approximately φ3 μμm). The Faraday cups 851 areprovided for a narrow beam measure a beam profile by driving theturntable 54 step by step, while the Faraday cups 852 for a wide beammeasure a total amount of current. The Faraday cups 851, 852 are mountedon the wafer carrying surface 541 such that their top surfaces arecoplanar with the upper surface of the wafer W carried on the carryingsurface 541. In this way, the primary electron beam emitted from theelectron gun 721 is monitored at all times. This is because the electrongun 721 cannot emit a constant electron beam at all times but varies inits emission intensity as it is used over a period of time.

Alignment Controller

The alignment controller 87 aligns the wafer W with the electron-opticaldevice 70 using the stage device 50, and it performs the control forrough alignment through wide view field observation using the opticalmicroscope 871 (a measurement with a lower magnification than themeasurement made by the electron-optical system); high magnificationalignment using the electron-optical system of the electron-opticalsystem 70; focus adjustment; inspecting region setting; patternalignment; and so on. The reason why the wafer is inspected at a lowmagnification using the optical microscope in this way is that analignment mark must be readily detected by an electron beam when thewafer is aligned by observing patterns on the wafer in a small fieldusing the electron beam for automatically inspecting patterns on thewafer.

The optical microscope 871 is disposed on the housing 30 (alternatively,it may be movably disposed within the housing 30), with a light source,not shown, being additionally disposed within the housing 30 foroperating the optical microscope. The electron-optical system forobserving the wafer at a high magnification shares the electron-opticalsystems (primary optical system 72 and secondary optical system 74) ofthe electron-optical device 70. The configuration may be generallyillustrated in FIG. 31. For observing a point of interest on a wafer ata low magnification, the X-stage 53 of the stage device 50 is moved inthe X-direction to move the point of interest on the wafer into a fieldof the optical microscope 871. The wafer is viewed in a wide field bythe optical microscope 871, and the point of interest on the wafer to beobserved is displayed on a monitor 873 through a CCD 872 to roughlydetermine a position to be observed. In this occurrence, themagnification of the optical microscope may be changed from a low to ahigh magnification.

Next, the stage system 50 is moved by a distance corresponding to aspacing δx between the optical axis O3—O3 of the electron-optical system70 and the optical axis O4—O4 of the optical microscope 871 to move thepoint on the wafer under observation, previously determined by theoptical microscope 871, to a point in the field of the electron-opticalsystem 70. In this occurrence, since the distance δx between the axisO₃-O₃ of the electron-optical system and the axis O₄-O₄ of the opticalmicroscope 871 is previously known (while it is assumed that theelectron-optical system 70 is deviated from the optical microscope 871in the direction along the X-axis in this embodiment, it may be deviatedin the Y-axis direction as well as in the X-axis direction), the pointunder observation can be moved to the viewing position by moving thestage system 50 by the distance δx. After the point under observationhas been moved to the viewing position of the electron-optical system70, the point under observation is imaged by the electron-optical systemat a high magnification for storing a resulting image or displaying theimage on the monitor 765 through the CCD 761.

After the point under observation on the wafer imaged by theelectron-optical system at a high magnification is displayed on themonitor 765, misalignment of the wafer in its rotating direction withrespect to the center of rotation of the turntable 54 of the stagesystem 50, and misalignment δθ of wafer in its rotating direction withrespect to the optical axis O₃—O₃ of the electron-optical system aredetected by a known method; misalignment of a predetermined pattern withrespect to the electron-optical system in the X-axis and Y-axis is alsodetected. Then, the operation of the stage system 50 is controlled toalign the wafer based on the detected values and data on an inspectionmark attached on the wafer or data on the shape of the patterns on thewafer which have been obtained in separation.

Vacuum Exhausting System

A vacuum exhausting system is comprised of a vacuum pump, a vacuumvalve, a vacuum gauge, a vacuum pipe and the like, and exhausts tovacuum an electron-optical system, a detector section, a sample chamber,a load-lock chamber and the like according to a predetermined sequence.In each of those sections, the vacuum valve is controlled so as toaccomplish a required vacuum level. The vacuum level is regularlymonitored, and in the case of irregularity, an interlock mechanismexecutes an emergency control of an isolation valve or the like tosecure the vacuum level. As for the vacuum pump, a turbo molecular pumpmay be used for the main exhaust, and a dry pump of Roots type may beused as a roughing vacuum pump. A pressure at an inspection spot (anelectron beam irradiating section) is practically in a range of 10⁻³ to10⁻⁵ Pa, but more preferably, in a range of 10⁻⁴ to 10⁻⁶ Pa.

Control System

A control system is mainly comprised of a main controller, a controllingcontroller, and a stage controller.

The main controller is equipped with a man-machine interface, throughwhich an operator manipulates the controller (a variety ofinstructions/commands, an entry of recipe, an instruction to start aninspection, a switching between an automatic inspection mode and amanual inspection mode, an input of all of the commands required in themanual inspection mode and so forth). In addition, the main controllermay further execute communication with a host computer of a factory, acontrol of a vacuum exhausting system, a control of a carrying and apositioning operations of a sample such as a wafer, an operation forsending commands and receiving information to/from the other controllersand/or stage controller and so forth. Further, the main controller hasthe following functions: to obtain an image signal from an opticalmicroscope; a stage vibration compensating function for compensating adeterioration in the image by feeding back a fluctuation signal of thestage to an electronic-optical system; and an automatic focal pointcompensating function for detecting a displacement of the sampleobservation point in the Z direction (in the axial direction of thesecondary optical system) and feeding back the detected displacement tothe electron-optical system so as to automatically compensate the focalpoint. Sending and receiving operations of the feedback signal to andfrom the electron-optical system and sending and receiving operations ofthe signal to and from the stage are performed via the controllingcontroller and the stage controller respectively.

The controlling controller is mainly responsible for the control of theelectron-optical system (an electron gun, a lens, an aligner, a controlof a high-precision power supply for a Wien filter or the like).Specifically, the controlling controller performs a control operation,for example, an automatic voltage setting for each of the lens systemsand the aligners in response to each operation mode (gang control), sothat a constant electron current may be regularly irradiated against theirradiation region even if the magnification is changed, and a voltageto be applied to each of the lens systems and the aligners may beautomatically set in response to each magnification.

The stage controller is mainly responsible for a control regarding tothe movement of the stage so that a precise movement in the X and the Ydirections may be performed in the order of μm (with tolerance of about±0.5 μm). Further, in the present stage, a control in the rotationaldirection (θ control) is also performed with a tolerance equal to orless than about ±0.3 seconds.

Cleaning of Electrode

In an electron beam apparatus according to the present invention beingoperated, a target substance floats due to a proximity interaction(charging of particles in the proximity of a surface) and is attractedto a high-voltage region; therefore, an organic substance will bedeposited on a variety of electrodes used for forming or deflecting anelectron beam. Since the insulating material gradually being depositedon the surface of the electrodes by the electric charge adverselyaffects the forming or deflecting mechanism for the electron beam,accordingly, this deposited insulating material must be periodicallyremoved. To remove the insulating material periodically, an electrodeadjacent to the region where the insulating material has been depositedis used to produce plasma of hydrogen, oxygen, fluorine, compositionincluding these elements, HF, O₂, H₂O, C_(M)F_(N) or the like, tomaintain the plasma potential in the space to the degree(several kV,e.g. 20–5 kV) so that sputtering is caused on the electrode surface,thereby allowing only the organic substance to be removed byoxidization, hydrogenation or fluorination.

Modified Embodiment of the Stage Device

FIG. 32 shows a modified embodiment of a vacuum chamber and XY stageadopted in the inspection apparatus according to the present invention.

A division plate 94 is attached onto an upper face of a Y directionallymovable unit 95 of a stage 93, wherein said division plate 914 overhangsto a considerable degree, approximately horizontally in the +Y directionand the −Y direction (the lateral direction in FIG. 32( b)), so thatbetween an upper face of an X directionally movable unit 96 and saiddivision plate 914 there is always provided a narrow gap 950 with smallconductance therebetween. Also, a similar division plate 912 is attachedonto the upper face of the X directionally movable unit 96 so as tooverhang in the ±X direction (the lateral direction in FIG. 32( a)), sothat a narrow gap 951 may be constantly formed between an upper face ofa stage table 97 and said division plate 912. The stage table 97 isfixedly secured onto a bottom wall within a housing 98 using a knownmethod.

In this way, since the narrow gaps 950 and 951 are constantly formedwherever the sample table 94 may move, and the gaps 950 and 951 canprevent the movement of a desorbed gas even if a gas is desorbed orleaked along the guiding plane 96 a or 97 a upon movement of the movableunit 95 or 96, any increase in pressure can be considerably reduced in aspace 924 adjacent to the sample against which the charged particlesbeam is irradiated.

In a side-face and an under face of the movable unit 95 and also in anunder face of the movable unit 96 of the stage 93, there are providedgrooves, for differential exhausting formed surrounding hydrostaticbearings 90, as shown in FIG. 56, and which work for vacuum-exhausting;therefore, in a case where narrow gaps 950 and 951 have been formed, thedesorbed gas from the guiding planes is mainly evacuated by thesedifferential exhausting sections. Because of this, the pressures inspaces 913 and 915 within the stage are kept at higher levels than thepressure within chamber C. Accordingly, if there are more portionsprovided for vacuum-exhausting the spaces 913 and 915, in addition tothe differential exhausting grooves 917 and 918, the pressure within thespaces 913 and 915 can be decreased, and the pressure rise of the space924 in the vicinity of the sample can be controlled so as to be keptlower. For this purpose, vacuum exhausting channels 91-1 and 91-2 areprovided. The vacuum exhausting channel 91-1 extends through the stagetable 97 and the housing 98 to communicate with an outside of thehousing 98. On the other hand, the exhausting channel 91-2 is formed inthe X directionally movable unit 96 and opens in an under face thereof.

It is to be noted that though arranging the division plates 912 and 914might cause a problem requiring the chamber C to be extended so that itdoes not interfere with the division plates, this can be improved byemploying division plates of stretchable material or structure. Oneembodiment in this regard may be suggested, which employs the divisionplates made of rubber or in a form of bellows, the ends portions ofwhich are fixedly secured respectively in the direction of movement sothat each end of the division plate 914 is secured to the Xdirectionally movable unit 96 and that of the division plate 912 to theinner wall of the housing 8.

FIG. 33 shows a second modified embodiment of a vacuum chamber and XYstage according to the present invention.

In this embodiment, a cylindrical divider 916 is disposed surroundingthe tip portion of the lens column or the charged particles beamirradiating section 72 so that a narrow gap may be produced between anupper face of a sample W and the tip portion of the lens column. In suchconfiguration, even if the gas is desorbed from the XY stage, andincreases the pressure within the chamber C, since a space 924 withinthe divider has been isolated by the divider 916 and exhausted with avacuum pipe 710, there could be generated a pressure difference betweenthe pressure in the chamber C and that in the space 924 within thedivider, thus control the pressure rise in the space 924 within thedivider 916 so that it is kept low. Preferably, the gap between thedivider 916 and the sample surface should be approximately some ten μmto some mm, depending on the pressure level to be maintained within thechamber C and in the surrounding of the irradiating section 72. It is tobe understood that the interior of the divider 916 is made tocommunicate with the vacuum pipe by the known method.

On the other hand, the charged particles beam irradiation apparatus maysometimes apply a high voltage of kV to the sample W, and so it isfeared that any conductive materials adjacent to the sample could causean electric discharge. In this case, the divider 916 made of insulatingmaterial such as ceramic may be used in order to prevent any dischargebetween the sample W and the divider 916.

It is to be noted that a ring member 94-1 arranged so as to surround thesample W (a wafer) is a plate-like adjusting part fixedly mounted on thesample table 94 and set to have the same height as the wafer so that amicro gap 952 may be formed throughout a full circle of the tip portionof the divider 916 even when the charged particles beam is beingirradiated against an edge portion of the sample such as the wafer.Thereby, whichever location on the sample W may be irradiated by thecharged particles beam, the constant micro gap 952 can always be formedat the tip portion of the divider 916 so as to maintain a stablepressure in the space 924 surrounding the lens body tip portion.

FIG. 34 shows a further modified embodiment of a vacuum chamber and anXY stage according to the present invention.

A divider 919 having a differential exhausting structure integratedtherein is arranged so as to surround the charged particles beamirradiating section 72 of a lens body 71. The divider 919 is cylindricalin shape and has a circular channel 920 formed inside thereof and anexhausting path 921 extending upwardly from said circular channel 920.Said exhausting path 921 is connected to a vacuum pipe 923 via an innerspace 922. A micro space as narrow as some ten μm to some mm is formedbetween the lower end of the divider 919 and the upper face of thesample W.

With such configuration, even if the gas is discharged from the stage inassociation with the movement of the stage resulting in an increase ofthe pressure within the chamber C, and eventually flows into the spaceof tip portion or the charged particles beam irradiating section 72, anyflow of gas is blocked by the divider 919, which has reduced the gapbetween the sample W and itself so as to make the conductance very low,thus reducing the flow rate. Further, since any gas that has entered canbe exhausted through the circular channel 920 to the vacuum pipe 923,there will be almost no gas remained to flow into the space 924surrounding the charged particles beam irradiating section 72;accordingly, the pressure of the space surrounding the charged particlesbeam irradiating section 72 can be maintained at the desired high vacuumlevel.

FIG. 35 shows a still further modified embodiment of a vacuum chamberand an XY stage according to the present invention.

A divider 926 is arranged so as to surround the charged particles beamirradiating section 72 in the chamber C, thus isolating the chargedparticles beam irradiating section 72 from the chamber C. This divider926 is coupled to a refrigerating machine 930 via a support member 929made of material of high thermal conductivity such as copper oraluminum, and is kept as cool as −100° C. to −200° C. A member 927 isprovided for blocking a thermal conduction between the cooled divider926 and the lens barrel and is made of material of low thermalconductivity such as ceramic, resin or the like. Further, a member 928is made of insulating material such as ceramic or the like and isattached to the lower end of the divider 926 so as to prevent anyelectric discharge between the sample W and the divider 926.

With such configuration, any gas molecules attempting to flow into thespace surrounding the charged particles beam irradiating section fromthe chamber C are blocked by the divider 926, and even if some moleculesmanage to flow into the section, they are frozen to be captured on thesurface of the divider 926, thus allowing the pressure in the space 924surrounding the charged particles beam irradiating section to be keptlow.

It is to be noted that various types of refrigerating machines may beused for the refrigerating machine in this embodiment, for example, acooling machine using liquid nitrogen, a He refrigerating machine, apulse-tube type refrigerating machine or the like.

FIG. 36 shows a further embodiment of a vacuum chamber and an XY stageaccording to the present invention.

The division plates 912 and 914 are arranged on both movable units ofthe stage 93 similarly to those illustrated i FIG. 32, and thereby, ifthe sample table 94 is moved to any location, the space 913 within thestage is separated from the inner space of the chamber C by thosedivision plates through the narrow gaps 950 and 951. Further, anotherdivider 916 similar to that as illustrated in FIG. 33 is formedsurrounding the charged particles beam irradiating section 72 so as toseparate a space 924 accommodating the charged particles beamirradiating section 72 therein from the interior of the chamber C with anarrow gap 952 disposed therebetween. Owing to this, upon movement ofthe stage, even if the gas adsorbed on the stage is desorbed into thespace 913 to increase the pressure in this space, the pressure increasein the chamber C is controlled so that it is kept low, and the pressureincrease in the space 924 is also kept even lower. This allows thepressure in the space 924 for irradiating the charged particles beam tobe maintained at a low level. Alternatively, employing the divider 919having the differential exhausting mechanism integrated therein asexplained with reference to FIG. 34, or the divider 926 cooled with therefrigerating machine as shown in FIG. 34 allows the space 924 to bemaintained stably with further lowered pressure.

According to the subject embodiment, the following effects may beexpected to obtain.

(a) The stage device can enhance accurate positioning within a vacuumatmosphere and the pressure in the space surrounding the chargedparticles beam irradiating location is hardly increased. That is, itallows the charged particles beam processing to be applied to the samplewith high accuracy.

(b) It is almost impossible for the gas desorbed or leaked from thehydrostatic bearing to go though the divider and reach the space for thecharged particles beam irradiating system. Thereby, the vacuum level inthe space surrounding the charged particles beam irradiating locationcan be further stabilized.

(c) It is harder for the desorbed gas to go through to the space for thecharged particles beam irradiating system, and it is easier to maintainthe stability of the vacuum level in the space surrounding the chargedparticles beam irradiating location.

(d) The interior of the vacuum chamber is partitioned into threechambers, i.e., a charged particles beam irradiation chamber, ahydrostatic bearing chamber and an intermediate chamber; each cancommunicate with the other via a small conductance. Further, the vacuumexhausting system is constructed so that the pressures in the respectivechambers are controlled sequentially, so that the pressure in thecharged particles beam irradiation chamber is the lowest, that in theintermediate chamber is in the middle range, and that in the hydrostaticbearing chamber is the highest. The pressure fluctuation in theintermediate chamber can be reduced by the divider, and the pressurefluctuation in the charged particles beam irradiation chamber can befurther reduced by another step of divider, so that the pressurefluctuation therein can be reduced substantially to a non-problematiclevel.

(e) The pressure increase upon movement of the stage can be controlledso that it is kept low.

(f) The pressure increase upon movement of the stage can be furthercontrolled so that it is kept even lower

(g) Since a defect inspection apparatus with highly accurate stagepositioning performance and with a stable vacuum level in the chargedparticles beam irradiating region can be accomplished, an inspectionapparatus with high inspection performance and without any fear ofcontamination of the sample can be provided.

(h) Since a defect inspection apparatus with highly accurate stagepositioning performance and with a stable vacuum level in the chargedparticles beam irradiating region can be accomplished, an exposingapparatus with high exposing accuracy and without any fear ofcontamination of the sample can be provided.

(i) Manufacturing the semiconductor by using the apparatus with highlyaccurate stage positioning performance and with a stable vacuum level inthe charged particles beam irradiating region allows a miniaturizedmicro semiconductor circuit to be formed.

Incidentally, it is apparent that the stage device shown in FIGS. 32–36can be applied to the stage device 50 shown in FIG. 1.

Further embodiments of the XY stage according to the present inventionwill now be described with reference to FIGS. 37 to 39. It is to benoted that the same reference numerals are used to designate the samecomponents common to both the embodiment according to the prior artshown in FIG. 55 and the embodiments according to the present invention.It is also to be appreciated that a term “vacuum” used in thisspecification means a vacuum as referred to in the field pertaining tothis art and does not necessarily refer to an absolute vacuum.

FIG. 37 shows another embodiment of the XY stage.

A tip portion of a lens body 71 or a charged particles beam irradiatingsection 72, which functions to irradiate a charged particles beamagainst a sample, is mounted on a housing 98 defining a vacuum chamberC. The sample “W” loaded on a table of an XY stage 93 movable in the Xdirection (the lateral direction in FIG. 3) is adapted to be positionedimmediately under the lens body 71. The XY stage 93 of high precisionallows the charged particles beam to be irradiated onto this sample Waccurately in any arbitrary location of the sample surface.

A pedestal 906 of the XY stage 93 is fixedly mounted on a bottom wall ofthe housing 98, and a Y table 95 movable in the Y direction (thevertical direction on paper in FIG. 37) is loaded on the pedestal 906.Convex portions are formed on both opposite sidewall faces (the left andthe right side faces in FIG. 37) of the Y table 95 respectively, each ofwhich projects into a concave groove formed on a side surface facing theY table in either of a pair of Y-directional guides 907 a and 907 bmounted on the pedestal 906. The concave groove extends alongapproximately the full length of the Y directional guide in the Ydirection. A top, a bottom and a side face of respective convex portionsprotruding into the grooves are provided with known hydrostatic bearings911 a, 909 a, 911 b and 909 b respectively, through which ahigh-pressure gas is expelled and thereby the Y table 95 is supported tothe Y directional guides 907 a and 907 b in non-contact manner so as tobe movable smoothly reciprocating in the Y direction. Further, a linearmotor 932 of known structure is arranged between the pedestal 906 andthe Y table 95 for driving the Y table 95 in the Y direction. The Ytable 95 is supplied with the high-pressure gas through a flexible pipe934 for supplying a high-pressure gas, and the high-pressure gas isfurther supplied to the above-described hydrostatic bearings 909 a to911 a and 909 b to 911 b though a gas passage (not shown) formed withinthe Y table. The high-pressure gas supplied to the hydrostatic bearingsis expelled into a gap of from several microns to some ten microns inthickness formed respectively between the bearings and the opposingguide planes of the Y directional guide so as to position the Y tableaccurately with respect to the guide planes in the X and Z directions(up and down directions in FIG. 37).

The X table 96 is loaded on the Y table so as to be movable in the Xdirection (the lateral direction in FIG. 37). A pair of X directionalguides 908 a and 908 b (only 908 a is illustrated) with the sameconfiguration as of the Y directional guides 907 a and 907 b is arrangedon the Y table 95 with the X table 96 sandwiched therebetween. Concavegrooves are also formed in the X directional guides on the sides facingthe X table and convex portions are formed on the side portions of the Xtable (side portions facing the X directional guides). The concavegroove extends approximately along the full length of the X directionalguide. A top, a bottom and a side face of respective convex portions ofthe X table protruding into the concave grooves are provided withhydrostatic bearings (not shown) similar to those hydrostatic bearings911 a, 909 a, 910 a, 911 b, 909 b and 910 b in the similar arrangements.A linear motor 933 of known configuration is disposed between the Ytable 95 and the X table 96 so as to drive the X table in the Xdirection. Further, the X table 96 is supplied with a high-pressure gasthrough a flexible pipe 931, and thus the high-pressure gas is suppliedto the hydrostatic bearings. The X table 96 is supported highlyprecisely with respect to the Y directional guide in a non-contactmanner by way of said high-pressure gas blowing out from the hydrostaticbearings to the guide planes of the X-directional guides. The vacuumchamber C is exhausted through vacuum pipes 919, 920 a and 920 b coupledto a vacuum pump of a known structure. Those pipes 920 a and 920 bpenetrate the pedestal 906 at the top surface thereof to open theirinlet sides (inner side of the vacuum chamber) in the proximity of thelocations to which the high-pressure gas is ejected from the XY stage93, so that the pressure in the vacuum chamber may be prevented to theutmost from rising up by the gas expelled from the hydrostatic bearings.

A differential exhausting mechanism 925 is arranged so as to surroundthe tip portion of the lens body 71 or the charged particles beamirradiating section 72, so that the pressure in a charged particles beamirradiation space 930 can be controlled so that it is sufficiently loweven if there exists high pressure in the vacuum chamber C. That is tosay, an annular member 926 of the differential exhausting mechanism 925,mounted so as to surround the charged particles beam irradiating section72, is positioned with respect to the housing 98 so that a micro gap (ofa thickness ranging from several microns to several hundred microns) 940can be formed between the lower face thereof (the surface facing to thesample) and the sample, and an annular groove 927 is formed in the lowerface thereof. That annular groove 927 is coupled to a vacuum pump or thelike (not shown), through an exhausting pipe 928. Accordingly, the microgap 940 can be exhausted through the annular groove 927 and theexhausting pipe 928, and if any gaseous molecules from the chamber Cattempt to enter the space 930 circumscribed by the annular member 926,they can be exhausted. Thereby, the pressure within the chargedparticles beam irradiation space 930 can be kept low and thus thecharged particles beam can be irradiated without any problems.

The size of said annular groove may be doubled or tripled, depending onthe pressure in the chamber C and the pressure within the chargedparticles beam irradiation space 930.

Typically, dry nitrogen is used as the high-pressure gas to be suppliedto the hydrostatic bearings. If available, however, a much higher-purityinert gas should preferably be used instead. This is because anyimpurities such as water, oil or fat included in the gas could stick onthe inner surface of the housing defining the vacuum chamber or on thesurfaces of the stage components leading to the deterioration in vacuumlevel, or could stick on the sample surface leading to the deteriorationin vacuum level in the charged particles beam irradiation space.

It should be appreciated that although typically the sample W is notplaced directly on the X table but may be placed on a sample tablehaving a function to detachably carry the sample and/or a function tomake a fine tuning of the position of the sample relative to the XYstage 93, an explanation therefor is omitted in the above descriptionfor simplicity due to the reason that the presence and structure of thesample table has no concern with the principal concept of the presentembodiment.

Since a stage mechanism of a hydrostatic bearing used in the atmosphericpressure can be used in the above-described charged particles beamapparatus mostly as it is, a stage having an equivalent level ofprecision with equivalent cost and size to those of the stage ofhigh-precision fitted for a use in the atmospheric pressure, which istypically used in an exposing apparatus or the likes, may beaccomplished for an XY stage to be used in a charged particles beamapparatus.

It should be also appreciated that the configuration and arrangement ofthe hydrostatic guide and the actuator (the linear motor) have been onlyillustratively explained in the above description, and any hydrostaticguides and actuators usable in the atmospheric pressure may beapplicable.

FIG. 38 shows an example of numerical values representative of the sizesof the annular member 926 and the annular groove formed in the annularmember 926 of the differential exhausting mechanism. It is to be notedthat in this example, the size of the annular groove is twice that ofthe structure of 927 a and 927 b, which are separated from each other inthe radial direction.

The flow rate of the high-pressure gas supplied to the hydrostaticbearing is in the order of about 20 L/min (in the conversion into theatmospheric pressure). Assuming that the vacuum chamber C is exhaustedby a dry pump having an exhaust velocity of 20000 L/min via a vacuumpipe having an inner diameter of 50 mm and a length of 2 m, the pressurein the vacuum chamber C will be about 160 Pa (about 1.2 Torr). At thattime, with the applied size of the annular member 926, the annulargroove and others of the differential exhausting mechanism as describedin FIG. 38, the pressure within the charged particles beam irradiationspace 930 can be controlled to 10⁻⁴ Pa (10⁶ mTorr).

FIG. 39 shows a further embodiment of the XY stage. A vacuum chamber Cdefined by a housing 98 is connected with a dry vacuum pump 953 viavacuum pipes 974 and 976. An annular groove 927 of a differentialexhausting mechanism 925 is connected with an ultra-high vacuum pump ora turbo molecular pump 951 via a vacuum pipe 970 connected to an exhaustport 928. Further, the interior of a lens body 71 is connected with aturbo molecular pump 952 via a vacuum pipe 971 connected to an exhaustport 710. Those turbo molecular pumps 951 and 952 are connected to thedry vacuum pump 953 through vacuum pipes 972 and 973. (In FIG. 39, thesingle dry vacuum pump is used to serve both as a roughing vacuum pumpof the turbo molecular pump and as a pump for vacuum exhausting of thechamber, but multiple dry vacuum pumps of separate systems may beemployed for exhausting, depending on the flow rate of the high-pressuregas supplied to the hydrostatic bearings of the XY stage, the volume andinner surface area of the vacuum chamber and the inner diameter andlength of the vacuum pipes.)

A high-purity inert gas (N₂ gas, Ar gas or the like) is supplied to ahydrostatic bearing of an XY stage 93 through flexible pipes 931 and932. The gaseous molecules expelled from the hydrostatic bearing arediffused into the vacuum chamber and exhausted by the dry vacuum pump953 through exhaust ports 919, 920 a and 920 b. Further, the gaseousmolecules that have entered the differential exhausting mechanism and/orthe charged particles beam irradiation space are sucked from the annulargroove 927 or the tip portion of the lens body 72 through the exhaustingports 928 and 710 to be exhausted by the turbo molecular pumps 951 and952; then, after having been exhausted by the turbo molecular pumps, thegaseous molecules are further exhausted by the dry vacuum pump 953.

In this way, the high-purity inert gas supplied to the hydrostaticbearing is collected in the dry vacuum pump and then exhausted.

On the other hand, the exhaust port of the dry vacuum pump 953 isconnected to a compressor 954 via a pipe 976, and the exhaust port ofthe compressor 954 is connected to flexible pipes 931 and 932 via pipes977, 978 and 979 and regulators 961 and 962. As a result of thisconfiguration, the high-purity inert gas exhausted from the dry vacuumpump 953 is compressed again by the compressor 954 and then the gas,after being regulated to an appropriate pressure by the regulators 961and 962, is supplied again to the hydrostatic bearings of the XY stage.

In this regard, since the gas to be supplied to the hydrostatic bearingsis required to be as highly purified as possible in order not to haveany water contents or oil and fat contents included therein, asdescribed above, the turbo molecular pump, the dry pump and thecompressor must have structures that prevent any water contents or oiland fat contents from entering the gas flow path. It is also consideredeffective for a cold trap, filter or the like (960) to be provided alongthe outlet side piping 977 of the compressor so as to trap anyimpurities such as water, oil or fat contents included in thecirculating gas and prevent them from being supplied to the hydrostaticbearings.

This may allow the high purity inert gas to be circulated and reused,and thus allows the high-purity inert gas to be saved, while the inertgas would not remain desorbed into a room where the present apparatus isinstalled, thereby eliminating a fear that any accidents such assuffocation or the like would be caused by the inert gas.

It is to be noted that a circulation piping system is connected with thehigh-purity inert gas supply system 963, said system 963 serving notonly to fill up, with the high-purity inert gas, all of the circulationsystems including the vacuum chamber C, the vacuum pipes 970 to 975, andthe pipes in compression side 976 to 980, prior to the commencement ofthe gas circulation, but also to supply gas if the flow rate of thecirculation gas decreases for some reason.

Further, a single dry vacuum pump 953, if provided with a function tocompress to a level equal to or greater than the atmospheric pressure,may be used as both the dry vacuum pump 953 and the compressor 954.

Further, as to the ultra-high vacuum pump to be used for exhausting thelens body, other pumps including an ion pump and a getter pump may beused instead of the turbo molecular pump. It is to be noted that in thecase where reservoir type pumps are used, it is prohibited to buildcirculation systems in those areas. It is also evident that instead ofthe dry vacuum pump, other type of dry pumps, for example, a dry pump ofdiaphragm type, may be used.

FIG. 40 schematically shows a typical optical system and a detector of acharged particles beam apparatus of an embodiment according to thepresent invention. Though the optical system is provided in the lensbody 71, these optical system and detector are illustrated only as anexample, but the other optical systems and detectors may be employed ifrequired. An optical system 760 of the charged particles beam apparatuscomprises a primary optical system 72 for irradiating a chargedparticles beam against a sample W loaded on a stage 50 and a secondaryoptical system 74 into which secondary electrons emanated from thesample are to be introduced. The primary optical system 72 comprises anelectron gun 721 for emitting the electron, a lens systems composed oftwo stages of electrostatic lenses 722 for converging the electronemitted from the electron gun 721, a deflector 730, a Wien filter or anE×B separator 723 for deflecting the charged particles beam so as for anoptical axis thereof to be directed to perpendicular to a surface of anobject, and a lens system composed of two stages of electrostatic lenses724, wherein those components of the primary optical system 72 arearranged in the order with the electron gun 721 at the topmost locationso that the optical axis of the charged particles beam is inclined tothe line normal to a surface of the sample W (a sample surface) as shownin FIG. 40. The E×B deflecting system 723 comprises an electrode 723-1and a magnet 723-2.

The secondary optical system 74 is an optical system to which thesecondary electrons emanated from the sample W are introduced, whichcomprises a lens system composed of two stages of electrostatic lenses741 disposed in an upper side of the E×B type deflecting system of theprimary optical system. A detector 761 detects the secondary electronssent through the secondary optical system 74. Since the structures andfunctions of respective components of said optical systems 760 and saiddetector 761 are similar to those in the prior art, a detaileddescription thereof should be omitted.

The charged particles beam emitted from the electron gun 721 isappropriately shaped in a square aperture below the electron gun,contracted by the lens system of two stages of lenses 722, and then,after the optical axis thereof is adjusted by the deflector 730, thecharged particles beam is formed into an image of 1.25 mms square on adeflection principal plane of the E×B deflecting system 723. The E×Bdeflecting system 723 is designed such that an electric field and amagnetic field are crossed within a plane orthogonal to a normal line ofthe sample, wherein when the relationship among the electric field, themagnetic field and the energy of electrons satisfies a certaincondition, the electrons are advanced straight ahead, and for any caseother than the above, the electrons are deflected into a predetermineddirection depending on said mutual relationship among the electricfield, the magnetic field and the energy of electrons. In FIG. 40, therelationship is set so that the charged particles beam from the electrongun can enter the sample W at right angles and the secondary electronsemanated from the sample can be advanced directly toward the detector761. The shaped beam, after being deflected in the E×B deflectingsystem, is contracted to ⅕ in size with the lens system composed of thelenses 724 to be projected onto the sample W. The secondary electronsemanated from the sample W, which have the information of a patternimage, are magnified by the lens systems composed of the lenses 724 andthe lenses 741 so as to form the secondary electron image on thedetector 761. These four stages of magnifying lenses, which are composedof the lens system of the lenses 724 forming a symmetrical tablet lensand the lens system of the lenses 741 also forming another symmetricaltablet lens, make up the lenses of no distortion.

According to the subject embodiment, the following effects may beexpected to obtain.

(A) Processing by the charged particles beam can be stably applied to asample on the stage by employing a stage having a structure similar toone of the hydrostatic bearing type which is typically used in theatmospheric pressure (a stage supported by the hydrostatic bearinghaving no differential exhausting mechanism).

(B) Affection on the vacuum level in the charged particles beamirradiation region can be minimized, whereby the processing by thecharged particles beam to the sample can be stabilized.

(C) An inspection apparatus that accomplishes positioning performance ofthe stage at low cost, with high precision and which provides a stablevacuum level in the irradiation region of the charged particles beam canbe provided.

(D) An exposing apparatus that accomplishes positioning performance ofthe stage at low cost, with high precision and which provides a stablevacuum level in the irradiation region of the charged particles beam canbe provided.

(E) A micro semiconductor circuit can be formed by manufacturing thesemiconductor using an apparatus which accomplishes positioningperformance of the stage with high precision and provides a stablevacuum level in the irradiation region of the charged particles beam.

Modified Embodiment of the Inspection Apparatus

FIG. 41 shows a schematic configuration of a defect inspection apparatusaccording to the modified embodiment of the present invention. Thisdefect inspection apparatus is explained above, i.e., a projective typeinspection apparatus, which comprises: an electron gun 721 for emittinga primary electron beam; an electrostatic lens 722 for deflecting andforming the emitted primary electron beam; an E×B deflecting system 723for deflecting the correspondingly formed primary electron beam at afield where an electric field “E” and a magnetic field “B” cross atright angles, so that the beam impinges against a semiconductor wafer Wat an approximately right angle; an objective lens 724 for forming thedeflected primary electron beam into an image on the wafer W; a stage 50arranged in a sample chamber (not shown) allowed to be evacuated tovacuum and capable of moving within a horizontal plane with the waferloaded thereon; an electrostatic lens 741 in a projection system forprojecting at a predetermined magnification a secondary electron beamand/or a reflected electron beam emitted from the wafer W upon theirradiation of the primary electron beam to be formed into an image; adetector 770 for detecting the formed image as a secondary electronimage of the wafer; and a control section 1016 for controlling the wholeunit of the apparatus and for performing the process for detecting adefect in the wafer W based on the secondary electron image detected bythe detector 770, as well. It is to be noted that the presentspecification has designated said image as the secondary electron image,although said secondary electron image is actually affected by not onlythe secondary electrons but also the back scattered and reflectedelectrons.

Further, between the objective lens 724 and the wafer W, there isarranged a deflecting electrode 1011 for deflecting an incident angle ofthe primary electron beam onto the wafer W by the electric field or thelike. This deflecting electrode 1011 is connected to a deflectioncontroller 1012 for controlling the electric field of said deflectingelectrode. This deflection controller 1012 is connected to the controlsection 1016 to control the deflecting electrode 1011 so that theelectric field may be generated by said deflecting electrode 1011 inresponse to a command from the control section 1016. It is to be notedthat the deflection controller 1012 may be a voltage controller forcontrolling a voltage applied to the deflecting electrode 1011.

The detector 770 may have any arbitrary configuration so long as it canconvert the secondary electron image formed by the electrostatic lens741 into a signal capable of being processed later. For example, asshown in detail in FIG. 46, the detector 770 may comprise amulti-channel plate 751, a fluorescent screen 772, a relay opticalsystem 773, and an image sensor 774 composed of a plurality of CCDelements. The multi-channel plate 751 comprises a plurality of channelswithin the plate so as to generate more electrons during the secondaryelectrons formed into the image by the electrostatic lens 741 passingthrough those channels. That is, the multi-channel plate 751 amplifiesthe secondary electrons. The fluorescent screen 772 radiate fluorescenceby the amplified secondary electrons to convert the secondary electronsinto light (fluorescence). The relay lens 773 guides said fluorescenceto the CCD image sensor 774, and then said CCD image sensor 774 convertsthe intensity distribution of the secondary electrons on the surface ofthe wafer W to an electric signal, i.e., a digital image data for eachelement, which in turn is output to the control section 1016.

The control section 1016, as shown in FIG. 41, may be composed of ageneral-purpose computer or the like. This computer may comprise acontrol section main unit 1014 for executing various controls andoperations according to a predetermined program, a CRT 1015 fordisplaying processed results from the main unit 1014, and an inputsection 18 such as a mouse and a keyboard used by an operator forinputting a command; of course, said control section 1016 may becomposed of a piece of hardware working exclusively as a defectinspection apparatus, namely a work station, or the like.

The control section main unit 1014 may comprise various controlsubstrates such as a CPU, RAM, ROM, a hard disk, and a video substrate,which are not illustrated. A secondary electron image storage region1008 is allocated memory such as RAM or that on a hard disk, for storingthe electric signal received from the detector 770, i.e., the digitalimage data for the secondary electron image of the wafer W. Further, onthe hard disk, there is a reference image storage section 1013 forstoring beforehand reference image data for wafers having no defects.Still further, on the hard disk, in addition to the control program forcontrolling the whole unit defect inspection apparatus, a defectdetection program 1009 is stored for reading the secondary electronimage data from the storage region 1008 and automatically detecting adefect in the wafer W based on said image data according to thepredetermined algorithm. This defect detection program 1009, as will bedescribed in more detail later, has a function that enables it toperform a matching of the reference image read out from the referenceimage storage section 1013 with an actually detected secondary electronimage in order to automatically detect any defective parts, so that itmay indicate a warning to the operator when it determines there is adefect. In this regard, the CRT 1015 may be designed to also display thesecondary electron image 1017 on the display section thereof.

Then, the operation of the defect inspection apparatus according to themodified embodiment will be exemplarily described referring to the flowcharts of FIGS. 43 to 45.

First of all, as shown in the flow of the main routine of FIG. 43, thewafer W to be inspected is placed on the stage 50 (step 1300). In thisregard, the way of setting the wafer W may be such that each of aplurality of wafers W contained in a loader is set on the stage 50automatically one by one as explained above.

Then, images for a plurality of regions to be inspected are respectivelyobtained, which are displaced one from another while being superimposedpartially one on another on the XY plane of the surface of the wafer W(Step 1304). Each of said plurality of regions to be inspected, fromwhich the image is to be obtained, is a rectangular region as designatedby reference numerals 1032 a, 1032 b, . . . 1032 k, . . . , each ofwhich is observed to be displaced relative to another while beingpartially superimposed on each another around the inspection pattern1030 of the wafer as shown in FIG. 47. For example, 16 pieces of images1032 for the regions to be inspected (the images to be inspected) may beobtained as shown in FIG. 42. Herein, for the image as shown in FIG. 42,each square contained in the rectangular region corresponds to one pixel(or a block, whose unit is greater than the unit of pixel), and amongthose squares, shaded ones correspond to the imaged area of the patternon the wafer W. This step 1304 will be described in more detail laterwith reference to the flow chart of FIG. 44.

Then the process compares the image data for the plurality of regions tobe inspected, which have been obtained at Step 1304, respectively withthe reference image stored in the storage section 1013 to look for anymatches (Step 1308 in FIG. 43), and determines whether or not there is adefect existing in the wafer inspection plane encompassed by saidplurality of regions to be inspected. This process performs what iscalled the matching operation between images, which will be explainedlater in detail with reference to the flow chart shown in FIG. 45.

If the result from the comparing process at Step 1308 indicates thatthere is a defect in the wafer inspection plane encompassed by saidplurality of regions to be inspected (Step 1312, affirmativedetermination), the process gives a warning to the operator indicatingthe existence of the defect (Step 1318). As for the way of warning, thedisplay section of the CRT 1015 may, for example, display a messagenotifying the operator that there is a defect, or at the same time mayadditionally display a magnified image 1017 of the pattern determined tohave the defect. Such defective wafers may be immediately taken out of asample chamber 31 and stored in another storage area separately fromthose wafers having no defects (Step 1319).

If the result from the comparing process at Step 1308 indicates thatthere is no defect in the wafer W (Step 1312, negative determination),the process determines whether or not there remain more regions to beinspected for the current wafer W currently treated as the inspectionobject (Step 1314). If there are more regions remaining for inspection(Step 1314, affirmative determination), the stage 50 is driven to movethe wafer W so that other regions to be further inspected are positionedwithin the irradiative region of the primary electron beam (Step 1316).Subsequently, the process goes back to Step 1302 to repeat similaroperations for said other regions to be inspected.

If no more regions remain to be inspected (Step 1314, negativedetermination), or after a drawing out processing of the defective wafer(Step 1319), the process determines whether or not the current wafertreated as the inspection object is the last wafer to be inspected, thatis, whether or not there are any wafers remaining for the inspection inthe loader, (though not shown) (Step 1320). If the current wafer is notthe last one (Step 1320, negative determination), the wafers inspectedalready are stored in a predetermined storage location, and a new waferwhich has not been inspected yet is set instead on the stage 50 (Step1322). Then, the process goes back to Step 302 to repeat similaroperations for said wafer. In contrast, if the current wafer is the lastone (Step 320, affirmative determination), the wafer just inspected isstored in the predetermined storage location to end the whole process.

Then, the process flow of step 1304 will now be described with referenceto the flow chart of FIG. 44.

In FIG. 44, first of all, an image number “i” is set to the initialvalue “1” (Step 1330). This image number is an identification numberassigned serially to each of the plurality of images for the regions tobe inspected. Secondary, the process determines an image position(X_(i), Y_(i)) for the region to be inspected as designated by the setimage number i (Step 1332). This image position is defined as a specificlocation within the region to be inspected for bounding said region, forexample, a central location within said region. Currently, i=1 definesthe image position as (X₁, Y₁), which corresponds, for example, to acentral location of the region to be inspected 1032 a as shown in FIG.47. The image position has been determined previously for every imageregion to be inspected, and stored, for example, in the hard disk of thecontrol section 1016 to be read out at Step 1332.

Then, the deflection controller 1012 applies a potential to thedeflecting electrode 1011 (Step 1334 in FIG. 44) so that the primaryelectron beam passing through the deflecting electrode 1011 of FIG. 41may be irradiated against the image region to be inspected in the imageposition (X_(i), Y_(i)) determined at Step 1332.

Then, the electron gun 721 emits the primary electron beam, which goesthrough the electrostatic lens 722, the E×B deflecting system 723, theobjective lens 724 and the deflecting electrode 1011, and eventuallyimpinges upon a surface of the set wafer W (Step 1336). At that time,the primary electron beam is deflected by an electric field generated bythe deflecting electrode 1011 so as to be irradiated onto the waferinspection surface 1034 covering the whole image region to be inspectedat the image position (X_(i), Y_(i)). When i=1, the region to beinspected is 1032 a.

The secondary electrons and/or the reflected electrons (hereafterreferred exclusively to as “secondary electrons” for simplicity) areemitted from the region to be inspected, to which the primary electronbeam has been irradiated. Then, the generated secondary electron beam isformed into an image on the detector 770 at a predeterminedmagnification by the electrostatic lens 741 of a magnifying projectionsystem. The detector 770 detects the imaged secondary electron beam, andconverts it into an electric signal for each detecting element, i.e.,digital image data (Step 1338). Then, the detected digital image datafor the image number i is sent to the secondary electron image storageregion 1008 (Step 1340).

Subsequently, the image number i is incremented by 1 (Step 1342), andthe process determines whether or not the incremented image number (i+1)is greater than a constant value “i_(MAX)” (Step 1344). This i_(MAX) isthe number of images to be inspected that must be obtained, which is“16” for the above example of FIG. 42.

If the image number i is not greater than the constant value i_(MAX)(Step 1344, negative determination), the process goes back to Step 332again, and determines again the image position (X_(i+1), Y_(i+1)) forthe incremented image number (i+1). This image position is a positionmoved from the image position (X_(i), Y_(i)) determined by the previousroutine by a specified distance (ΔX_(i), ΔY_(i)) in the X directionand/or Y direction. The region to be inspected in the example of FIG. 41is at the location (X₂, Y₂), i.e., the rectangular region 1032 bindicated with the dotted line, which has been moved from the position(X₁, Y₁) only in the Y direction. It is to be noted that the value for(ΔX_(i), ΔY_(i)) (i=1, 2, . . . i_(MAX)) may have been appropriatelydetermined from the data indicating practically and experimentally thedisplacement of the pattern 1030 on the wafer inspection surface 1034from the field of view of the detector 770 and the number and the areaof the regions to be inspected.

Then, the operations for Step 1332 to Step 1342 are repeated in orderfor i_(MAX) regions to be inspected. These regions to be inspected arecontinuously displaced while being partially superimposed one on anotheron the wafer inspection surface 1034 so that the image position after ktimes of movements (X_(k), Y_(k)) corresponds to the inspection imageregion 1032 k, as shown in FIG. 47. In this way, the 16 pieces ofinspection image data illustrated in FIG. 42 are captured in the imagestorage region 1008. It is observed that a plurality of images 1032obtained for the regions to be inspected (i.e., inspection image)contains partially or fully the image 1030 a of the pattern 1030 on thewafer inspection surface 1034, as illustrated in FIG. 42.

If the incremented image number i has become greater than i_(MAX) (Step1344, affirmative determination), the process returns from thissubroutine and goes to the comparing process in the main routine of FIG.37 (Step 1308).

It is to be noted that the image data that has been transferred to thememory at Step 1340 is composed of intensity values of the secondaryelectrons for each pixel (so-called, raw data), and this data may bestored in the storage region 1008 after having been processed throughvarious operations in order for use in performing the matching operationrelative to the reference image in the subsequent comparing process(Step 1308 of FIG. 43). Such operations include, for example, anormalizing process for setting the size and/or density of the imagedata to be matched with the size and/or the density of the referenceimage data, or a process for eliminating as noise an isolated group ofelements having a number of pixels not greater than the specifiednumber. Further, the image data may be converted by means of datacompression into a feature matrix that contains extracted features ofthe detected pattern rather than the simple raw data, as long as it doesnot negatively affect the accuracy in detection of the highly precisepattern. Such a feature matrix includes, for example, an m×n featurematrix, in which a two-dimensional inspection region composed of M×Npixels is divided into m×n (m<M, n<N) blocks, and respective sums ofintensity values of the secondary electrons of the pixels contained ineach block (or the normalized value defined by dividing said respectivesums by the total number of pixels covering all of the regions to beinspected) should be employed as respective components of the matrix. Inthis case, the reference image data also should have been stored in thesame representation. The image data in the context used in theembodiment of the present invention includes, of course, simple raw databut also includes any image data having features extracted by anyarbitrary algorithms as described above.

The process flow for Step 1308 will now be described with reference tothe flow chart of FIG. 45.

First of all, the CPU in the control section 1016 reads the referenceimage data out of the reference image storage section 1013 (FIG. 41)into a working memory such as RAM or the like (Step 1350). Thisreference image is identified by reference numeral 1036 in FIG. 42.Then, the image number “i” is reset to 1 (Step 1352), and the processreads out from the storage region 1008 the inspection image data havingthe image number i into the working memory (Step 1354).

Then, the read-out reference image data is compared with the data of theimage i for matching to calculate a distance value “D_(i)” between thereference and image i (Step 356). This distance value D_(i) indicates asimilarity level between the reference image and the image to beinspected “i”, wherein a greater distance value indicates a greaterdifference between the reference image and the inspection image. Anyunit of measurement representative of the similarity level may be usedfor said distance value D₁. For example, if the image data is composedof M×N pixels, the process may consider that the secondary electronintensity (or the measurement representative of the feature) for eachpixel is a position vector component of M×N dimensional space, and thencalculate a Euclidean distance or a correlation coefficient between thereference image vector and the image i vector in the M×N dimensionalspace. It will be easily appreciated that any distance other thanEuclidean distance, for example, the urban area distance may becalculated. Further, if the number of pixels is huge, which increasesthe amount of calculation significantly, then the process may calculatethe distance value between both image data represented by the m×nfeature vector as described above.

Subsequently, it is determined whether the calculated distance valueD_(i) is smaller than a predetermined threshold Th (Step 1358). Thisthreshold Th is determined experimentally as a criterion for judgingsufficient matching between the reference image and the inspectionimage.

If the distance value D_(i) is smaller than the predetermined thresholdTh (Step 1358, affirmative determination), the process determines thatthe inspection plane 1034 of said wafer W has “no defect” (Step 1360)and returns from this subroutine. That is, if there is found at leastone image among those inspection images matching to the reference image,the process determines there is “no defect”. Accordingly, since thematching operation is not necessarily be applied to every inspectionimage, high-speed judgment becomes possible. As for the example of FIG.42, it is observed that the image to be inspected at column 3 of the row3 approximately matches the reference image without any offset thereto.

When the distance value D_(i) is not smaller than the threshold Th (Step1358, negative determination), the image number i is incremented by 1(Step 1362), and then it is determined whether or not the incrementedimage number (i+1) is greater than the predetermined value i_(MAX) (Step1364).

If the image number i is not greater than the predetermined valuei_(MAX) (Step 1364 negative determination), the process goes back toStep 1354 again, reads out the image data for the incremented imagenumber (i+1), and repeats similar operations.

If the image number i is greater than the predetermined value i_(MAX)(Step 1364, affirmative determination), then the process determines thatsaid inspection plane 1034 of said wafer W has “a defect existing” (Step1366), and returns from the subroutine. That is, if any one of theimages to be inspected does not approximately match the reference image,the process determines that there is “a defect existing”.

Although the defect inspection apparatus has been described withspecific embodiments, it is to be apprehended that the present inventionis not limited only to the above embodiments but also may be modifiedarbitrarily and preferably without departing from the scope and spiritof the present invention.

For example, although the description has illustratively employed asemiconductor wafer W as a sample to be inspected, the sample to beinspected in the present invention is not limited to this. Anything maybe selected as the sample as long as it can be inspected for defects byusing the electron beam. For example, the object to be inspected may bea mask with an exposure pattern formed thereon.

Further, the present invention may be applied not only to an apparatuswhich detects any defects with charged particle beams other thanelectrons but also to any apparatus which allows images to be obtainedfor inspecting the sample for defects.

Still further, the deflecting electrode 1011 may be disposed not onlybetween the objective lens 724 and the wafer W but also at any arbitrarylocation as long as the irradiation region of the primary electron beamcan be controlled. For example, the deflecting electrode 1011 may bedisposed between the E×B deflecting system 723 and the objective lens724, or between the electron gun 721 and the E×B deflecting system 723.Further, the E×B deflecting system 723 may control the deflectingdirection by controlling the field generated thereby. That is, the E×Bdeflecting system 723 may function also as the deflecting electrode1011.

Further, although in the above embodiment, either one of matchingbetween the pixels and matching between the feature vectors can beemployed for the matching operation between image data, they may also becombined. For example, a much faster and more precise matching processcan be constructed by two-step matching, in which firstly a high-speedmatching is performed with the feature vectors, which requires feweroperations, and subsequently a more precise matching is performed withmore detailed pixel data for the images to be inspected that have beenfound to be quite similar.

Still further, although in the embodiments of the present invention, theposition mismatch for the image to be inspected has been resolved onlyby displacing the irradiating region of the primary electron beam, thepresent invention may be combined with a process for retrieving anoptimal matching region on the image data before or during the matchingprocesses (e.g., first detecting the regions having higher correlationcoefficients and then performing the matching). This can improve theaccuracy of defect detection, because the major position mismatch forthe image to be inspected is rectified by displacing the irradiatingregion of the primary electron beam, while the relatively minor positionmismatch can be absorbed subsequently with the digital image processing.

Yet further, although the configurations for an electron beam apparatusfor defect detection have been illustratively shown in FIG. 41, theelectron optical systems or the like may be preferably and arbitrarilymodified as long as they function well. For example, although theelectron beam irradiation means (721, 722, 723) shown in FIG. 41 hasbeen designed so as to irradiate the primary electron beam onto thesurface of the wafer W at a right angle from above, the E×B deflectingsystem 723 may be omitted so that the primary electron beam maydiagonally impinge upon the wafer W.

Still further, the flow in the flow chart of FIG. 43 is also not limitedto the illustrated one. For example, although in the embodiment theprocess does not further perform defect detection in any other regionsof the sample that have been determined to have a defect at Step 1312,the flow may be modified so that the overall area can be inspected forany defects to be detected. Yet further, if the irradiating area of theprimary electron beam can be expanded so as to cover almost the entirearea of the sample with one shot of irradiation, Steps 1314 and 1316 canbe omitted.

As described above in detail, according to the defect inspectionapparatus of the modified embodiment, since a defect in the sample canbe detected by first obtaining respective images of a plurality ofregions to be inspected, which are displaced from one another whilebeing partially superimposed one on another on the sample, and comparingthose images of the regions to be inspected with the reference image,therefore an advantageous effect can be provided in that the accuracy ofdefect detection can be maintained.

Further, according to the device manufacturing method of the modifiedembodiment, since defect detection is performed by using a defectinspection apparatus as described above, another advantageous effect canbe provided in that the yield of the products can be improved and faultyproducts need not be delivered.

Other Embodiments of an Electron Beam Apparatus

Further, there is another method attempting to solve the problemassociated with this projecting method, in which a plurality of electronbeams is used to scan a sample surface in an observation region whileperforming a scanning operation in two dimensions (X-Y directions, thatis, raster scanning), and a projecting type of secondaryelectron-optical system has been employed therefor. That methodpreserves the benefits of the above-described projecting method, whilestill solving the problems associated with the projecting method byusing a plurality of electron beams for scanning, said problem includingthe facts: (1) charging may easily occur on a sample surface because ofirradiation of electron beam being made at once; and (2) the inspectionspeed is hard to improve since an electron beam current obtained by thismethod is limited (to around 1.6 μA). That is, since the electron beamirradiating point is moved, electric charge is more likely to escape andthereby the charging is decreased. Further, increasing the number of theplurality of electron beams makes it easier to increase the currentvalue. It has been observed in the embodiment which uses four electronbeams, that the current for one electron beam is 500 nA (with a beamdiameter of 10 μm) and a total of 2 μA can be obtained. The number ofbeams of electrons can be easily increased to about 16, and in thatcase, it is possible in principle to obtain a total of 8 μA. As forscanning by a plurality of electron beams, it is only required that theirradiation amount using the plurality of electron beams is kept uniformover the irradiation region, so that scanning is not limited to theabove-mentioned raster scanning but can use other scanning patterns suchas Lissajous' figures. Accordingly, the direction in which the stagemoves is not required to be normal to the scanning direction of theplurality of electron beams.

Electron Gun (Electron Beam Source)

A thermal electron beam source has been employed as an electron beamsource to be used in this embodiment. The electron emitting (emitter)material is L_(a)B₆. Other materials may be used as long as they have ahigh melting point (lower vapor pressure at higher temperature) and alow work function. Two methods are used in order to obtain a pluralityof electron beams. In one method, a single electron beam is derived froma single emitter (with one projection) and then is passed through a thinplate having a plurality of apertures formed therein (an aperture plate)to obtain a plurality of electron beams, while in the other method, asingle emitter is provided with a plurality of projections formedtherein, from which a plurality of electrons is directly derived. Eithercase takes advantage of the property that an electron beam tends to beemitted from the tip portion of a projection. Electron beam sources ofother methods, for example, an electron beam of thermal field emissiontype, may also be usable.

It is to be appreciated that the thermal electron beam source is one inwhich the electron emitting member is heated to emit an electron, whilethe thermal field emission electron beam source is one in which a highelectric field is applied to the electron emitting member to emitelectrons and further the electron emitting section is heated so as tostabilize emission of electrons.

FIG. 48A is a schematic view of an electron beam apparatus according tothe embodiment of the present invention. On the other hand, FIG. 48B isa schematic plan view illustrating an aspect of a plurality of primaryelectron beams scanning a sample. An electron gun 721 adapted to beoperative with a space-charge limitation forms a multi-beam designatedby reference numeral 711. The multi-beam 711 comprises primary electronbeams 711 a composed of 8 circular beams arranged on a circle.

A plurality of primary electron beams 711 a generated in the electrongun 721 is focused by using lenses 722-1 and 722-2, and after beingdirected by an E×B deflecting system 723 consisting of an electrode723-1 and a magnet 723-2, is made enter onto a sample W at a rightangle. The multi-beam 711, which is composed of the plurality of primaryelectron beams 711 a focused on the sample W by a primary optical systemcomprising those elements 711, 722-1, 722-2 and 723 and lenses 724-1 and724-2, is used to scan the sample W by a two-step deflecting systemdisposed downstream to the lens 722-2 (not shown but included in theprimary optical system).

The scanning of the sample W is performed in the x-axis direction withthe principal surface of the objective lens 724-2 as the deflectioncenter. As shown in FIG. 48B, the primary electron beams 711 a of themulti-beam 711 are spaced apart from one another on the circle anddesigned so that when they are projected on the y-axis orthogonal to thex-direction or the scanning direction, the distances between any twoadjacent primary electron beams 711 a are equal (measured from thecenter of each primary electron beam) on the y-axis. At that time, thoseadjacent two primary electron beams 711 a may be seperated from eachother, in contact with each other, or partially overlapped.

As shown in FIG. 48B, since the primary electron beams 711 a forming themulti-beam 711 are arranged to be seperated from one another, thecurrent density threshold value for each of the primary electron beams711 a, that is, the critical current density value which would not causeany charges on the sample W, may be maintained at level equivalent tothat in the case of a single circular beam being used, thereby keepingthe S/N ratio high. Further, owing to the primary electron beams 711 abeing kept apart in this manner, the space-charge effect should also below.

On the other hand, the multi-beam 711 can scan the sample W over theentire surface of a field of view 713 at a uniform density in one-timescanning. This allows images to be formed with high throughput and thusreducing the inspection time. In FIG. 48B, the reference numeral 711designates the multi-beam at the starting point of scanning, while thereference numeral 711 a designates the multi-beam at the end point ofscanning.

The sample W is loaded on a sample table (not shown). During a scanningoperation in the x-direction (for example, scanning with the scanningwidth of 200 μm), the sample table is driven to move continuously alongthe y-direction so as to cross with the scanning direction “x” at aright angle. This accomplishes raster scanning. A drive means (notshown) is provided for moving the table with the sample loaded thereon.

Those secondary electrons, which emanated from the sample W at the timeof scanning and emitted in different directions, are accelerated by theobjective lens 724-2 in the optical axial direction and resultantly thesecondary electrons that have been emitted from the respective points inthe different directions are respectively focused to be narrower, andthe spacing between images is increased through the lenses 724-1, 741-1and 741-2. A secondary electron beam 712 that has been formed afterpassing through the secondary optical system including those lenses724-1, 724-2, 741-1 and 741-2 is projected on the acceptance plane of adetector 761 and focused into an enlarged image of the field of view.

The detector 761 included in a light optical system uses a MCP (MicroChannel Plate) to multiply the secondary electron beam, and themultiplied secondary electron beam is then converted into an opticalsignal by a scintillator, which is further converted into an electricsignal in a CCD detector. According to the electric signal from the CCD,a two-dimensional image for the sample W can be formed. Each of theprimary electron beams 711 a is designed to have a size equal to orgreater than an area equivalent to two pixels in the CCD pixels.

Operating the electron gun 721 under the condition of the space-chargelimitation allows the shot noise to be reduced by about one digit incomparison with the case of operation under the condition of thetemperature limitation. Accordingly, the shot noise associated with thesecondary electric signal can be also reduced by one digit, and therebya signal with better S/N ratio may be obtained.

According to the electron beam apparatus of this embodiment, since thecurrent density threshold value for primary electron beams that wouldnot cause any charges on the sample may be maintained at an equivalentlevel to that in the case of a single circular beam being used, theinspection time may be shortened by forming images with higherthroughput while preventing any deterioration in the S/N ratio.

Further, the device manufacturing method according to the presentinvention allows the yield thereof to be improved by evaluating thewafer at the ends of respective wafer processes using the electron beamapparatus described above.

FIG. 49A is a schematic diagram illustrating in detail the configurationof an electron beam apparatus of the embodiment shown in FIG. 48A. Fourelectron beams 711 (711-1, 711-2, 711-3 and 711-4) emitted from anelectron gun 1 are shaped appropriately in an aperture diaphragm NA-1,formed into an image of elliptical shape of 10 μm×12 μm on a deflectionprincipal plane of a Wien filter 723 by two stages of lenses 722-1 and722-2, and used to make a raster-scanning operation in the verticaldirection on paper of the drawing by the deflector 730 so as to beformed into an image for uniformly covering a rectangular region of 1mm×0.25 mm with four electron beams as a whole. The plurality ofelectron beams that has been deflected by the E×B 723 are focused into across-over at the NA diaphragm, contracted into ⅕ in size with a lens724, and then irradiated and projected so as to cover a sample W in anarea of 200 μm×50 μm and so as to be normal to the sample surface(referred to as Koehler illumination). Four electron beams 712, eachbeing emanat from the sample and having a data of pattern image (asample image F), are magnified by the lenses 724, 741-1 and 741-2, andare altogether formed into a rectangular image (a magnified projectionimage F′) synthesized by four electron beams 712 as a whole on a MCP767. The magnified projection image F′ synthesized from the secondaryelectron beams 712 is made to be sensitized up to 10,000 times inintensity by the MCP 767, converted into the light by a fluorescencesection 767 and further converted by a TDI-CCD 762 into an electricsignal synchronized with a speed of a serial movement of the sample,which signal is obtained by an image displaying section 765 as a seriesof images and is output to a CRT or the like.

An electron beam irradiating section is required to irradiate the samplesurface more uniformly and further reduce unevenness during irradiationin a rectangular or elliptical shape with the electron beam, and is alsorequired to irradiate the electron beam to the irradiation region with ahigher current in order to increase throughput. An uniformity inirradiation associated with the prior art is about ±10%, where theuniformity in the image contrast is greater, while the electron beamirradiation current is as low as about 500 nA in the irradiation region,which has the problem in that a higher throughput is hard accomplish.Further, in comparison with a scanning electron microscope (SEM) method,the present method has been problematic in that a disorder in imageformation due to a charging is more likely to occur because a largerimage observation region is exposed at once to the electron beamirradiation.

An irradiation method of the primary electron beam according to thepresent embodiment is shown in FIG. 49B. The primary electron beam 711is composed of four electron beams 711-1, 711-2, 711-3 and 711-4, eachof which is in the shape of an ellipse of 2 μm×2.4 μm and each one beingcapable of raster-scanning a rectangular region of 200 μm×12.5 μm, whichare added together without overlapping one another, thus accomplishingthe rectangular region of 200 μm×50 μm as a whole to be irradiated. Thebeam at the position 711-1 reaches the position 711-1′ within a finitetime and returns to the position immediate below the position 711-1 (inthe direction 202) offset by a beam-spot diameter (10 μm) with almost notime loss, and moves to the position immediately below the position711-1′ (in the direction 711-2′ ) parallel to the line 711-1 to 711-1′again within a finite time as before, and after repeating the samemovements to scan one quarter (200 μm×12.5 μm) of the rectangularirradiation region indicated by the dotted line, the beam returns backto the original position 711-1 and repeats the same movement at highspeed. Other electron beams 711-2 to 711-4 repeat the scanning similarlyto and at the same speed as the electron beam 711-1 and thus those beamsaltogether irradiate the rectangular region (200μ×50 μm) in the drawinguniformly at high speed. As long as the uniform irradiation is achieved,a method other than said raster scanning might be used. For example, thescanning may be performed so as to draw a Lissajous figure. Accordingly,the direction of the stage movement is not limited to the direction A asindicated in the drawing. That is, the direction of the stage movementis not required to be normal to the scanning direction (fast scanning inthe lateral direction in the drawing). The embodiment has accomplishedthe irradiation with electron beam irradiation uniformity of about ±3%.With the irradiation current of 250 nA per electron beam, four electronbeams were used and the total current of 1.0 μA was obtained on thesample surface (two times as high as that by the prior art). Increasingthe number of electron beams allows the current to be increased and ahigher throughput to be obtained. Further, since the irradiation pointis smaller than that in the prior art (about 1/80 in area) and alsomoving, the charging is successfully controlled so that it is no greaterthan 1/20 of that in the prior art.

Although not illustrated in the drawing, the present apparatuscomprises, in addition to the lenses, a limit field stop, a deflector(an aligner) having four or more poles for adjusting the axis of theelectron beam, an astigmatism corrector (stigmator), and further units,such as a plurality of quadrupole lenses (four-pole lenses) for shapingthe beam form and the like, which are necessary for illuminating andfocusing the electron beam.

Device Manufacturing Method

Next, an embodiment of a method of manufacturing a semiconductor deviceaccording to the present invention will be described with reference toFIGS. 50 and 51.

FIG. 50 is a flow chart illustrating an embodiment of a method ofmanufacturing a semiconductor device according to the present invention.Manufacturing processes of this embodiment include the following mainprocesses:

(1) a wafer manufacturing process for manufacturing a wafer (or a waferpreparing process for preparing a wafer)(Step 1400);

(2) a mask manufacturing process for manufacturing masks to be usedduring the exposure (or mask preparing process for preparing masks)(Step1401);

(3) a wafer processing process for performing any processing treatmentnecessary for the wafer (Step 1402);

(4) a chip assembling process for cutting out those chips formed on thewafer one by one to make them operable (Step 1403); and

(5) a chip inspection process for inspecting finished chips (Step 1404).

The respective main processes are further comprised of severalsub-processes.

Among these main processes, the wafer processing process set forth in(3) exerts a critical effect on the performance of resultantsemiconductor devices. This process involves sequentially laminatingdesigned circuit patterns on the wafer to form a large number of chipswhich operate as memories, MPUs and so on. The wafer processing processincludes the following sub-processes:

(A) a thin film forming sub-process for forming dielectric thin filmsserving as insulating layers and/or metal thin films for forming wiringsor electrodes, and the like(by using CVD, sputtering and so on);

(B) an oxidization sub-process for oxidizing the thin film layers andthe wafer substrate;

(C) a lithography sub-process for forming a resist pattern by usingmasks (reticles) for selectively processing the thin film layers and/orthe wafer substrate;

(D) an etching sub-process for processing the thin film layers and/orthe wafer substrate in accordance with the resist pattern (by using, forexample, dry etching techniques);

(E) an ion/impurity injection/diffusion sub-process;

(F) a resist striping sub-process; and

(G) a sub-process for inspecting the processed wafer;

As can be appreciated, the wafer processing process is repeated a numberof times depending on the number of required layers to manufacturesemiconductor devices which operate as designed.

FIG. 51A is a flow chart illustrating the lithography sub-process whichforms the core of the wafer processing process in FIG. 50. Thelithography sub-process includes the following steps:

(a) a resist coating step for coating a resist on the wafer on whichcircuit patterns have been formed in the previous process (Step 1500);

(b) an exposing step for exposing the resist (Step 1501);

(c) a developing step for developing the exposed resist to produce aresist pattern (Step 1502); and

(d) an annealing step for stabilizing the developed resist pattern (Step1503).

Since the aforementioned semiconductor device manufacturing process,wafer processing process and lithography process are well known, nofurther description is required.

When the defect inspection method and defect inspection apparatusaccording to the present invention are used in the inspectionsub-process set forth in (G), any semiconductor devices, even thosehaving miniature patterns, can be inspected at a high throughput, sothat a total inspection can also be conducted, thereby making itpossible to improve the yield rate of products and prevent defectiveproducts from being shipped.

Inspection Procedure

An inspection procedure in the inspection process (G) stated above isexplained as follows.

Generally, since an inspection apparatus using an electron beam isexpensive and the throughput thereof is rather lower than that providedby other processing apparatuses, this type of inspection apparatus iscurrently applied to a wafer after an important process (for example,etching, film deposition, or CMP (chemical and mechanical polishing)flattening process) to which it is considered that the inspection isrequired most.

A wafer to be inspected is, after having been positioned on anultra-precise X-Y stage through an atmosphere transfer system and avacuum transfer system, secured by an electrostatic chucking mechanismor the like, and then a detect inspection is conducted according to aprocedure as shown in FIG. 51B. At first, if required, a position ofeach die is checked and/or a height of each location is sensed, andthose values are stored. /In addition, an optical microscope is used toobtain an optical microscope image in an area of interest possiblyincluding defects or the like, which may also be used in, for example,the comparison with an electron beam image. Then, recipe informationcorresponding to the kind of wafer (for example, after which process theinspection should be applied; what is the wafer size, 20 cm or 30 cm,and so on) is entered into the apparatus, and subsequently, after adesignation of an inspection place, a setting of an electronic-opticalsystem and a setting of an inspection condition being established, adefect inspection is typically conducted in real time whilesimultaneously obtaining the image. A fast data processing system withan algorithm installed therein executes an inspection, such as thecomparisons between cells, between dies or the like, and any resultswould be output to a CRT or the like and stored in a memory, if desired.Those defects include a particle defect, an irregular shape (a patterndefect) and an electric defect (a broken wire or via, a bad continuityor the like); and the fast data processing system also can automaticallyand in realtime distinguish and categorize the defects according totheir size, or whether they are a killer defect (a critical defect orthe like which disables a chip). The detection of the electric defectmay be accomplished by detecting an irregular contrast. For example,since a location having a bad continuity would generally be positivelycharged by an electron beam irradiation (about 500 eV) and thereby itscontrast would be decreased, the location of bad continuity can bedistinguished from normal locations. The electron beam irradiation meansin that case designates an electron beam source (means for generatingthermal electron, UV/photoelectron) with lower potential (energy)arranged in order to emphasize the contrast by a potential difference,in addition to the electron beam irradiation means used for a regularinspection. Before the electron beam being irradiated against theobjective region for inspection, the electron beam having that lowerpotential (energy) is generated and irradiated. In the case of aprojecting method in which the object can be positively chargedparticles by the irradiation of the electron beam, the electron beamsource with lower potential is not necessarily arranged separately,depending on the specification of the system for the method. Further,the defect may be inspected based on the difference in contrast (whichis caused by the difference in flowability of elements depending on theforward or backward direction) created by, for example, applying apositive or negative potential relative to a reference potential to awafer or the like. This electron beam generation means may be applicableto a line-width measuring apparatus and also to an aligning accuracymeasurement.

1. An inspection apparatus for inspecting an object to be inspected byirradiating either of charged particles or electromagnetic waves ontosaid object to be inspected, said apparatus comprising: amini-environment chamber for supplying a clean gas as a laminar downflowto said object to be inspected to prevent dust from contacting saidobject to be inspected, said mini-environment chamber includes a gassupply unit including a cleaning filter such as HEPA or ULPA filter forcreating said clean gas, a pre-aligner for aligning the orientation ofsaid object to be inspected in a rotation direction about the axis ofsaid object for rough alignment thereof; a main housing includingworking chamber for inspecting said object to be inspected, said chambercapable of being controlled to have a vacuum atmosphere said workingchamber includes; a beam generating means for generating either of saidcharged particles or said electromagnetic waves as a beam; an electronoptical system including an objective lens for guiding and irradiatingsaid beam onto said object to be inspected held in said working chamber,detecting secondary charged particles emanated from said object to beinspected by a secondary charged particle detector and introducing saidsecondary charged particles to an image processing system; a stagedevice for operatively holding said object to be inspected so as to bemovable with respect to said beam, wherein said stage device permitshighly accurate alignment of said object to be inspected by comprising aholder within said working chamber which holds said object in thex-direction, y-direction with respect to said beam, and in the directionabout the axis normal to the object supporting surface of said holder, aloader housing disposed between said mini-environment chamber and saidmain housing, said loader housing includes a first loading chamber and asecond loading chamber; wherein said first loading chamber includes arack for placing the object thereon, a shutter device for opening andclosing a first door connecting said first loading chamber and saidmini-environment chamber, and a second shutter device for opening andclosing a second door connecting said first loading chamber and saidsecond loading chamber, said first loading chamber is adapted to becontrollable so as to have a vacuum atmosphere; wherein said secondloading chamber includes an arm which is movable to said rack forreceiving the object and transporting the object to said main housing,said second loading chamber being held in a high vacuum atmosphere; avibration isolator for supporting said main housing and said loaderhousing thereon; and an electrode located in the proximity of the objectwhich is irradiated with said beam, an electric charge detector fordetecting an electric charge of said electrode, and a power source forgenerating a voltage to said electrode corresponding to the electriccharge of said electrode for offsetting said electric charge of saidelectrode.
 2. An inspection apparatus according to claim 1, furthercomprising: an alignment controller for observing the surface of saidobject to be inspected with respect to said electron-optical system tocontrol the alignment, said alignment controller includes an opticalmicroscope for effecting a rough alignment of the object to be inspectedin a wide field before a high magnification alignment for inspection ismade by said electron-optical system, wherein said inspection apparatusis a projection type electron beam inspection apparatus and includes anelectrode between said object to be inspected and said objective lens soas to control the electric field between said object and said objectivelens.
 3. An inspection apparatus according to claim 1, furthercomprising: a vacuum exhausting system for generating the vacuumatmosphere in said working chamber, said vacuum exhausting systemcomprises a vacuum pump including a turbo molecular pump as a mainexhaust pump and a dry pump of a Roots type as a roughing vacuum pump,and an interlock mechanism, wherein the vacuum level in said workingchamber is monitored; and in the case of irregularity, said interlockmechanism executes an emergency control to secure the vacuum level at asafe level, wherein said inspection apparatus is a projection typeelectron beam inspection apparatus and includes an electrode betweensaid object to be inspected and said objective lens so as to control theelectric field between said object and said objective lens.
 4. Aninspection apparatus according to claim 1 wherein said mini-environmentchamber is provided therein with a sensor for observing the cleanlinesswithin said mini-environment chamber such that the inspection apparatusis shut down when the cleanliness is below a predetermined level,wherein said inspection apparatus is a projection type electron beaminspection apparatus and includes an electrode between said object to beinspected and said objective lens so as to control the electric fieldbetween said object and said objective lens.
 5. An inspection apparatusaccording to claim 1, further comprising: a precharge unit forirradiating a charged particle beam or photo electrons onto said objectto be inspected placed in said working chamber to reduce variations incharge on said object to be inspected, wherein said precharge unitcomprises a UV lamp coated with a photoelectron emission material foremitting a photoelectron the energy thereof being 0 eV–10 eV.
 6. Aninspection apparatus according to claim 1, wherein said apparatusincludes an apparatus for irradiating a charged particle beam againstthe surface of the object to be inspected loaded on an XY stage whilemoving said object to a desired position in vacuum atmosphere, said XYstage being provided with a non-contact supporting mechanism by means ofa hydrostatic bearing and a vacuum sealing mechanism by means ofdifferential exhausting, and a divider is provided for making theconductance smaller between the charged particle beam irradiating regionand the hydrostatic bearing support section, so that there is a pressuredifference produced between said charged particle beam irradiatingregion and said hydrostatic bearing support section, wherein saidinspection apparatus is a projection type electron beam inspectionapparatus and includes an electrode between said object to be inspectedand said objective lens so as to control the electric field between saidobject and said objective lens.
 7. An inspection apparatus according toclaim 1, wherein said electron optical system includes: an B×B separatorfor deflecting said secondary charged particle toward said detector by afield where an electric field and a magnetic field cross at right angle,said B×B separator includes at least a pair of electrodes for generatingthe electric field and a pair of electrodes for generating the magneticfield, wherein said inspection apparatus is a projection type electronbeam inspection apparatus and includes an electrode between said objectto be inspected and said objective lens so as to control the electricfield between said object and said objective lens.
 8. An inspectionapparatus according to claim 1, wherein said beam irradiated on saidobject comprises a multi-beam, wherein said inspection apparatus is aprojection type electron beam inspection apparatus and includes anelectrode between said object to be inspected and said objective lens soas to control the electric field between said object and said objectivelens.
 9. An inspection apparatus according to claim 1, furthercomprising: an electrode provided between said objective lens and saidobject to be inspected which is supplied with a predetermined voltagelower than that applied to said object to be inspected, wherein saidinspection apparatus is a projection type electron beam inspectionapparatus and includes an electrode between said object to be inspectedand said objective lens so as to control the electric field between saidobject and said objective lens.
 10. An inspection apparatus according toclaim 1, further comprising: a precharge unit for irradiating chargedparticles on said object to be inspected to prevent variations in theamount of charge on the surface of the object, the voltage for theenergy of the charged particles is set to a landing voltage lower than30 eV, wherein said inspection apparatus is a projection type electronbeam inspection apparatus and includes an electrode between said objectto be inspected and said objective lens so as to control the electricfieldbetween said object and said objective lens.
 11. An inspectionapparatus for inspecting an object to be inspected by irradiating eitherof charged particles or electromagnetic waves onto said object to beinspected, said apparatus comprising: a main housing including a workingchamber for inspecting said object to be inspected, said chamber capableof being controlled to have a vacuum atmosphere, said working chamberincludes; a beam generating means for generating either of said chargedparticles or said electromagnetic waves as a beam; an electron opticalsystem including an objective lens for guiding and irradiating said beamonto said object to be inspected held in said working chamber, detectingsecondary charged particles emanated from said object to be inspected bya secondary charged particle detector and introducing said secondarycharged particles to an image processing system; and an electrodelocated in the proximity of the object which is irradiated with saidbeam, an electric charge detector for detecting an electric charge ofsaid electrode, and a power source for generating a voltage to saidelectrode corresponding to the electric charge of said electrode foroffsetting said electrode charge of said electrode.
 12. An inspectionapparatus according to claim 11, wherein said electric charge detectormeasures amount of electric charge of said electrode after capturingsecondary charged particle by said secondary charged particle detector.